It is inevitable.

The reality of a major league season is that it is almost impossible to begin and end a year with the same starting nine. Opening Day regulars endure injuries or performance declines, and players who were expected to have limited playing time assert themselves to become regulars. It is part of the natural life cycle of any team, something with which the Sox are entirely familiar.

In 2003, the Red Sox opened the year with a logjam at first, third and DH, with the likes of Shea Hillenbrand, Bill Mueller, Jeremy Giambi, Kevin Millar and David Ortiz fighting for a finite number of at-bats. It took a couple months, but the dust settled, and Ortiz emerged as a superstar, Mueller became an All-Star and Millar became a fixture.

In 2004, there was the trade that sent Nomar Garciaparra packing and brought Orlando Cabrera into the mix.

In 2005, midnight struck for Mark Bellhorn, resulting in a trade for Tony Graffanino, while Millar was slowly replaced by John Olerud at first.

In 2006, widespread injuries led to late-season trials for players such as Dustin Pedroia, Wily Mo Pena, David Murphy, Carlos Pena and others.

In 2007, Jacoby Ellsbury usurped Coco Crisp as the everyday center fielder in the postseason.

In 2008, Crisp returned the favor, in a season when Jed Lowrie emerged in place of the injured Julio Lugo as an everyday shortstop. And, of course, there was the midyear swap that sent Manny Ramirez packing and brought on board his replacement in Jason Bay.

In 2009, Nick Green and then Alex Gonzalez ended up manning shortstop for the Sox, in a year when the Sox could not keep anyone healthy at the position. Victor Martinez was acquired in a trade to take on the Sox’ primary catching responsibilities.

A year ago, widespread injuries to Jacoby Ellsbury, Dustin Pedroia, Mike Cameron and Kevin Youkilis (along with woeful performance by Jeremy Hermida) opened the door for Ryan Kalish, Darnell McDonald and Bill Hall to become lineup regulars.

It is part of the rhythm of the baseball calendar, and for the second time this year, the Sox have reached a point of potential transition. Just as Jed Lowrie wrestled the starting shortstop job from Marco Scutaro at the beginning of the season, so, too, does it now appear that Josh Reddick is primed to lay claim to increased playing time in right field at the expense of J.D. Drew.

Carl Crawford is slated to return from the disabled list on Monday in Baltimore. With his return, the timeshare arrangement that featured Reddick and Drew starting in the outfield corners against right-handed pitchers and McDonald as well as another right-handed hitter (first Mike Cameron, then Yamaico Navarro) handling left-handed starters will go by the wayside.

The Sox will face a particularly noteworthy choice in deciding between Drew and Reddick. In terms of performance, there is really no question about what the Sox should do. Drew remains an outstanding defensive right fielder, though as Reddick (who is considered a legitimate big league option at all three outfield positions) demonstrated with his leaping catch against the left field wall on Sunday night, he, too, has above-average defensive tools.

And offensively, there is no real contest between the two, at least at this stage of the year. Drew has drawn his walks and seen his pitches, but his impact with the bat pales in comparison to what Reddick has delivered.

In roughly 30 percent of the at-bats that Drew has had this year, Reddick has matched the incumbent right fielder in extra-base hits (11), and has nearly matched his RBI total (Drew has 22, Reddick has 17). And while his lack of patience has been a concern in the past, the 24-year-old has shown significant progress in that regard as well.

He has eight walks in 82 plate appearances this year, and on Sunday, he walked multiple times in the same game for the first time as a big leaguer. He has seen 3.76 pitchers per plate appearance and has been putting himself in good hitter's counts. He won’t be confused for Drew, but he is also looks less and less like someone who has to hit like Vlad Guerrero to succeed in the majors.

And so, Reddick has done everything in his power to assert himself. Drew is in the last year of his five-year, $70 million contract. He is more than a year (dating to last July 2) into a period when he has been a limited offensive contributor. Reddick, meanwhile, is performing at a level that has made it nearly impossible for the Sox to remove him from the lineup.

Sox manager Terry Francona is always careful about making the decision to shift from a proven veteran to a young player amidst a hot streak. Nonetheless, the matter has become fairly straightforward to navigate.

“No dilemma. If that’s considered a dilemma, I’d like to have a lot of them,” Francona said of the issue of managing the playing time of Drew and Reddick, comparing it to the emergence of Lowrie at Scutaro's expense earlier this year. “At some point, when he’s hot like that, the kid’s got to play. It’s kind of like Lowrie earlier in the year. You’re not doing your team a service. He’s been terrific. And to be honest with you, until we’re there, I don’t know how to make that work perfectly, but we’re just going to try to win. Whoever we think can help us win, we’ll play.”

Right now, Reddick has forced the team’s hand. Some matchups will no doubt play into the decision about who to play on a day-to-day basis, but with Drew’s struggles suggesting that his track record is a decreasingly useful predictor of his future performance, that can only go so far.

All of that said, it would be a mistake to assume that right field will be Reddick’s job from this point forward. Just as the normal rhythms of a baseball calendar suggest that a team will rarely go through a year with the same lineup, so, too, is it common to see a young Sox player assert himself but then drift back to earth.

For that matter, it remains possible that Reddick could be used as trade bait. Given that the Sox do have Drew as well as — if/when healthy — Ryan Kalish as alternatives in right field, the Sox could take advantage of a time when Reddick’s value is at its highest to leverage him to address areas of need.

Nonetheless, for now it would appear to be Reddick’s opportunity to thrive. Thus far, he has done just that.