As Greg Bird returns, how have hitters with labrum surgery fared in the past?

If there’s one sure thing for the 2017 Yankees, it’s that there are no sure things. From the rotation that is only 60% filled to a game of musical chairs between catcher, designated hitter, and first base, it’s anyone’s guess what the Yankees’ roster and record will look like next season. Continuing on the trend of unknowns is the team’s projected starting first baseman Greg Bird.

Bird burst onto the scene in 2015 with 46 games of high-octane offense, complete with a .261/.343/.529 line and outstanding 137 wRC+. Unfortunately, 2016 was a lost season due to surgery for a torn labrum he re-injured that offseason. Shoulder ailments are noted for being very hard to treat and make a full recovery from. Luckily, torn labrums don’t end careers for batters the same way they can for pitchers, though that’s not to say the road to recovery will be easy.

In fact, shoulder injuries have developed a reputation for having a power-sapping effect on many hitters in their first season back—an effect that was thrust into the spotlight after Matt Kemp struggled upon returning from labrum surgery. The problem that Kemp, and many other hitters have run into, is regaining their previous mechanics with a weak and untrustworthy shoulder after a season off. As important as it is to rebuild strength, relearning swing mechanics can prove the most challenging part of the rehabilitation process, especially when the injury is to the lead shoulder in a swing (unfortunately, this is the case for Bird).

So while a hitter returning from any long-term injury carries a decent level of risk, one on his way back from shoulder (or labrum) surgery is particularly hard to evaluate. Trying to use Bird’s 2015 to project his 2017 might largely be pointless, since his performance will hinge more on that shoulder than it will his true talent level. With that in mind, it may be most helpful to use past examples of labrum tears to form an expectation for Bird. Should we expect a significant offensive downtick, with less power? Or could more than a full year of rehab (and at-bats in the Arizona Fall League, which have gone very well so far) be enough for Bird to regain his previous form?

To find a solid precedent for Bird, I looked at every batter that underwent labrum surgery from 2007 to 2015 and proceeded to log at least 50 games the following season. Unfortunately, there weren’t many examples—17 to be specific. I looked at their performance (measured by wRC+ for overall offensive value and slugging percentage for power output) the season before their surgery, and recorded the same metrics for the two seasons (if available) following the surgery.

Among the 17 examples, I didn’t find a strong correlation between pre- and post-injury output. On average, batters didn’t see their offensive output tick down at all in their first or second seasons back. In fact, their wRC+ and SLG marks stayed fairly consistent. That doesn’t mean all batters had fairly steady production, though. The lack of correlation points toward a fairly wide variance among each hitter. Some, such as Adam LaRoche and Coco Crisp actually improved, while others, like Hanley Ramirez and Luke Scott, stayed relatively steady, and an unlucky bunch, including Matt Kemp and Melvin Upton Jr., struggled in their first year back.

One interesting note is that age seems to play some factor in future performance. I picked (admittedly arbitrary) intervals for age, 23-27 and 28-33, and found that the younger group slightly struggled in their first season back (6% decrease in offense), while the older group improved a tick (9% increase). Neither value is very large, but this trend is worth keeping an eye on, and perhaps suggests that veterans have less trouble regaining their mechanics than younger players.

On the whole, though, it’s hard to draw much of a conclusion from this study. We can probably say that Bird is at a disadvantage by being younger and having injured his lead shoulder, but he’s also going to have more time than most do to rehab, and seeing live pitching in the Arizona Fall League should be a big help. I feel comfortable saying that I have no idea what Bird will do next season—a sentiment most will agree with—though labrum surgery for a hitter may not be quite as damning as many think.