Grady Sizemore's presence on the Red Sox brings up all kinds of questions. Will he be healthy? What will his role be? How well is he going to play in his first season back on the field since 2011? As of now, we can't know the answer to the first, and we don't yet know the answer to the second. We can make plenty of informed guesses about the last of those three, however, using Sizemore's own career as well as a litany of projections.
Let's start with what Sizemore has already accomplished. From his debut in 2004 through 2009, ages 21 through 26, the Indians center fielder produced a .275/.367/.485 line, good for a 124 OPS+. He missed time with injury in 2009, limiting him to 106 games, and while he was still productive he wasn't his best that year, finishing with a 110 OPS+. During those years, there was only one center fielder who bested Sizemore's production, minimum 2,500 plate appearances, and that's potential Hall of Famer Carlos Beltran, who was still in his peak with his age-27 through age-32 campaigns. Coincidentally, Beltran is also a player whose career was derailed by the need for microfracture surgery in his knee. Since returning in mid-2010, Beltran was slower afield and on the bases, but he hasn't missed a beat at the plate and owns a 133 OPS+ over the last three seasons, with a 109 mark in 64 2010 contests.
Now, that's not to say Sizemore is going to pick right up where he left off the last time he was healthy. Beltran, as stated, is a Cooperstown-caliber bat who was still incredibly successful into his 30s before injury slowed him down for parts of two years. Sizemore has missed two full seasons, so there's some comparison there, but suggesting anyone is directly akin to Beltran is problematic. The talent was obviously comparable when both were healthy and in their mid-20s, but since Sizemore has missed all of his late-20s, we're not sure if he was in line to age nearly as well as Beltran did. Still, we can use Beltran as a guide to a degree. The 109 OPS+ he produced in his first season back as a 33-year-old seems attainable for Sizemore, who managed a 96 mark in 2011 when he still clearly wasn't right, and was at 110 in his first season dealing with injury.
Something in the 110 range also makes sense just in terms of a cautious projection for someone with Sizemore's career path. He was far superior to that in his mid-20s, but now he's 31, and this spring marks the most baseball he's played in the last two years. There's bound to be a bit of game rust or fatigue that works in and against him, keeping him from reaching what he might actually be capable of: it's what happened to Beltran, even, as it took him until his first full season back to be the guy he used to be once more.
Sizemore's projections do not necessarily agree with that, however. All they see is a player who has missed the last two years, and wasn't all that good in 2010 or 2011. Steamer projects Sizemore to a .238/.293/.383 line with an 83 wRC+ (essentially the Fangraphs' version of OPS+). ZiPS forecasts Sizemore to a similar line with an 81 wRC+. For reference, Beltran's 2010 campaign discussed above produced a 106 wRC+ -- these systems do not see Sizemore anywhere near that.
Baseball Prospectus' PECOTA is more optimistic, at least, projecting Sizemore to bat .241/.318/.408, good for a .261 True Average (.260 is league average). It's not a great year by any means, but it's well ahead of the pace either Steamer or ZiPS sees. PECOTA works injuries into its forecasts, though, so maybe it should be expected that it would pop out something more aesthetically pleasing for the recovering Sizemore.
The other thing about PECOTA is that it has percentile forecasts -- the line above is just the most-likely, average outcome for Sizemore. PECOTA sees much darker futures for Sizemore possible: at the 30th percentile, he's barely better than a replacement-level hitter, and at the 10th, he looks like someone who is going to be forced into early retirement. On the other side, though, PECOTA envisions a productive Sizemore: at the 70th percentile, he's at a .254/.334/.432 line and .274 TAv, while at the 90th -- the most optimistic -- he's all the way up at .280/.364/.478, good for a .299 TAv, a figure that would fit in well with his healthy peak years.
If you've made it this far, you've likely realized that no one is quite sure what Sizemore is going to be if he manages to stay on the field. It's not difficult to envision him coming back healthy after two years off and going back to what he once was, but that doesn't mean it's the most probable outcome. It's easy to see him failing as ZiPS and Steamer have forecasted, but the projections PECOTA spit out are reasonable enough, as is the idea that he'll have a slower -- yet productive -- return campaign like Beltran did back in 2010.
The Red Sox are in a position to find out what he is, though, since they have the insurance policy of Jackie Bradley Jr. around should Sizemore start and flop in the role. If Sizemore does come back like Beltran did, but returns to form by mid-season after shaking off the rust, then the Red Sox will have themselves a serious replacement for Jacoby Ellsbury. If not, and Sizemore can't put it together for more than a couple of games at a time due to physical limitations -- or is just outright bad against regular season pitching -- then at least Bradley is around.