We’re through four games of this series and what do we actually know? Two things, really.

One, it’s becoming clearer that LeBron James’ supporting cast still has not proven it is ready for prime time yet. And two, that Rajon Rondo is one of the elite players in the NBA.

But there is still so much more to be discovered in a series where momentum seems to only last until the game tips off. The Cavaliers have this nasty habit of starting games slowly — until they didn’t in Game 3. The Celtics have had a season-long issue with closing out games — until they did it in Game 4.

What would happen if, for instance, both teams came out aggressively at the start of the game, and then, what if both teams continued to play that way for four quarters?

“Someone’s going to win a game when both teams are perfectly focused, when both teams are playing great,” Doc Rivers said Monday after his team had tied the best-of-seven series at two. “Someone’s still going to have to win that game and it might be Game 5.”

Or it might not. No one knows at this point which team is going to be the aggressor, and that’s really what this all comes down to. For all the hoopla regarding the, “Who will guard Rondo?” storyline, there have been very few major adjustments made in this series. The core things that were true before Game 1 are just as true now.

Take the Celtics defense from Game 3 to Game 4. In Game 3, they allowed the Cavs to shoot almost 60 percent. In Game 4, the number was 40 percent.

“We haven’t changed our defense,” Rivers said. “We just did our defense better.”

At this point in the series, everyone knows what to expect, with the one wrinkle emanating from the anticipated LeBron-Rondo matchup, but it’s still a matter of accomplishing it. 

“You’re talking about two heavyweights going at it,” Paul Pierce said. “Shots to the head. Shots to the body. You got to expect that. We’re still trying to find that edge where we can gain some momentum.”

So, as both teams try to take control of this series, here are five things to watch for in Game 5, which might feel a little bit familiar.

LEBRON VS. RONDO: IT’S ON (PROBABLY)

The Celtics have been waiting for this since about the time they put the finishing touches on the Miami Heat. Actually, they were probably thinking about this after they got locked into the No. 4 seed.

LeBron James said after Sunday’s game that it was time to explore — his word — the concept of having his MVP-self try to check Rajon Rondo. The Cavs have resisted, but on Monday, Mike Brown said he was going to give LeBron the go-ahead.

“We don’t care who guards Rondo,” Rivers said. “We’re going to still run out stuff. It’s not like we’re going to stop running our offense. We anticipated it. I’ve only talked about it for three games. We know it’s going to come at some point in this series. When it does we have to find a way of using Rondo and making sure he’s still the facilitator.”

Rondo, naturally, also expressed his nonchalance.

“It’s happened before,” he said. “LeBron is going to be LeBron. He’s a great help-defender so he’s definitely going to be helping. He’s a good defender. They did that a couple of years ago when Kobe [Bryant] was checking me in the Finals. So, I’m used to bigger guys giving me the shot and challenging me late because of their wingspan.”

But Rondo has come a long way since the 2008 Finals. He has figured out ways to combat the defense and still remain effective. Even in Game 3 when the Cavs caught the Celtics flat-footed by having Anthony Parker pressure Rondo the length of the floor, he still scored 18 points and had eight assists. It’s a measure of how far he’s come that a line like that would be considered sub-par.

Whoever guards Rondo, the Celtics want to get him moving toward the basket, whether it’s with pick and rolls, transition or ball movement. It remains to be seen if LeBron will guard Rondo for the entire game or pick his spots. But when he does it could have an effect on other Celtics, namely: Paul Pierce.

CAN PIERCE GET IT GOING?

One of the obvious reasons the Cavs have not used the LeBron strategy yet is that he has done a tremendous job of removing Pierce’s offense from the equation. The numbers for Pierce in this series are not encouraging — 18-for-50 from the floor, 4-for-22 from 3-point range.

Some of that is on Pierce. Rivers felt that there were times in Game 4 when Pierce didn’t press the advantage when he had a favorable matchup.

“When he gets the right matchups, he’s got to morph back into being Paul,” Rivers said. “That’s where we’re working on and we’ve got to get him more in those situations if we can.”

Pierce may have some more advantageous matchups if the Cavs use LeBron on Rondo. Parker is no slouch defensively, but he’s not nearly as physical a defender as James.

“That’s probably one of the reasons they haven’t, but they’re going to at some point,” Rivers said. “It may not be all game. It may be in the fourth quarter. It may be in the second half, out of timeouts. And we’ll be ready for it.”

Pierce said Monday that there is nothing physically wrong with him. He needs to stay out of early foul trouble, which has plagued him in this series. He also needs to be more aggressive when he does get his chances.

All that is true, but Pierce does deserve a little credit for not trying to do too much at the wrong time.

“We don’t want to sacrifice the entire offense or the team just to get Paul involved,” Rondo said. “Paul is just an unselfish player, so he’s not complaining about shots or that he’s only scoring 11 or 12 points. As long as we’re winning, he knows it’s a team sport. He’s very unselfish. It’s about sacrifices. Yesterday, I think Ray [Allen] got 21 shots up and myself. Maybe Paul gets 22 shots and maybe Ray and I only shoot four. It varies each game. If a guy has it going, you keep going to him.”

The Celtics probably need at least one vintage Pierce performance to pull this off. If the Cavs switch LeBron off him, there would be no better time for him to get it than in Game 5.

REBOUNDING IS KEY, PART V

In the Celtics two losses, the Cavs pulled in 11 offensive rebounds in each game. In their two wins, they allowed a combined nine offensive rebounds.

Beyond the obvious point that offensive rebounds leads to easy second-chance points, the Celtics have an offensive reason for clamping down on the defensive boards — it fuels their fast break.
“We can’t run without the ball,” Rivers said. “We can’t run if they score every time and they’re taking the ball out. We can’t run if we foul them every time and they’re shooting free throws. And we can’t run if they’re getting second shots. Those three things we have to try to stop.”

Last season, the Celtics were one of the best defensive rebounding teams in the league. This season they have been about league average. There are several reasons for that — age, injury, the fact that Rasheed Wallace was one of the worst rebounding big men in the NBA this season.

But the biggest reason may have been allowing dribble penetration, which leads to rotations, which lead to open spaces for offensive players to crash the glass.

The Celtics have played their defense better and that has helped tighten up on the boards. They have “helped the help,” as Kendrick Perkins likes to say. They also hit upon a novel approach in Game 4: Let the smallest guy on the court track down long rebounds.

The Cavs shoot a lot of jump shots. That tends to lead to long rebounds and that’s where Rondo is most dangerous. Rondo said after the game that the best way to start the fast break was if he got the rebound himself. It cuts out the middle man.

But rebounding is also about effort and the Celtics contested every loose ball in Game 4. That has to continue if they are going to win on the glass, and if they are going to win in Cleveland.

WHO STEPS UP FOR THE CAVS?

Mo Williams got a lot of mileage out of going off at the end of the third quarter in Game 1. True, it helped turn the momentum, but he hasn’t exactly been lighting it up, either before or after his scoring outburst. 

Since Game 1, Williams has scored just 29 points on 8-for-26 shooting and he didn’t make his first 3-pointer in the entire series until Game 4.

Shaquille O’Neal was basically a non-entity until Sunday’s game when he got virtually the entire Celtics front line into foul trouble.  

Antawn Jamison has been the most consistent of LeBron’s supporting cast, but aside from the Game 3 wipeout, he has averaged just over 12 points and seven rebounds. The Celtics can live with him getting 14 or 16 points.

James is so good and dominates so much of the action that it’s not imperative that everyone comes along for the ride in order for them to win. But the Celtics can’t allow more than one or two of the supporting players to compliment him.

“The key is going to be stopping guys like Mo Williams and Antawn Jamison,” Pierce said.

The pressure isn’t just on the players. It’s also on Brown to find the right combinations and the right buttons to push. The assumption all season was that his moment of truth would come against Orlando in the conference finals. If nothing else, the Celtics have accelerated Cleveland’s timetable.

DOES HOMECOURT MEAN ANYTHING?

The two teams have split the four games with each side winning one in the other’s building. Actually, there have been two blowouts in the other’s home building.

But, it’s worth pointing out that the home team has won both games that were decided in the fourth quarter and that has to count for something.

“We know it’s going to be a tough place to play back in Cleveland,” Pierce said. “It’s going to be very difficult. I think we’re going to put our hard hats on, and hopefully try to steal another win.”

The Celtics are certainly confident about the prospects. They were one of the better road teams during the regular season and they have two big road wins already on their postseason resume.

The Celtics obviously have to win at least once in Cleveland and you can make an argument that it would be far easier to try to steal a Game 5 than a Game 7.

“The pressure is on them now and also on us,” Rondo said. “So there’s no one-way street now as far as to where the pressure is. I’m fairly confident we can go into Cleveland and get a win. We definitely have to be focused.”

Focused, aggressive, determined; pick your adjective. Whoever has done that has won the game and forced the other to live on the edge and raise their game. Now that we’re tied, Game 5 has the feel of a showdown. We’ll see if it delivers on that promise.