There was some chatter recently about whether Brandon Guyer could/should replace Desmond Jennings. It's easy to see what got people thinking about it. Here are their 2014 stats.
To date, Guyer has been the better offensive player in 2014, and he's done it in a way that fans find more appealing. He's struck out less (16% compared to 20%). hit for a higher average, and been on base more often.
Of course, there's an obvious problem with that line of thinking. It's something so obvious that it bores people, so we rarely write about it, but maybe we should.
Yes, Brandon Guyer has been marginally better offensively than Desmond Jennings, but in a sample size that's too small to draw conclusions from. And a large chunk of Guyer's advantage comes from a statistic, batting average on balls in play, that we know to be almost completely unreliable in even a full season's worth of plate appearances. Both Jennings and Guyer are fast, athletic guys. They can both likely earn a few more infield singles than the average player, so it wouldn't be a shock for them to post above-average BABIPs (average is around .300). But no, you cannot conclude from what we've seen that Guyer's true-talent BABIP is 30 points better than Jennings's. To take a more Bayesian approach -- one that incorporates what we've seen this season from the two players into what we already knew about them -- just look at the rest of season projections available on FanGraphs. ZiPS has Jennings pegged for a 109 wRC+ and Guyer for a 102 wRC+.
Another difference is their usage. Jennings is an every day player, while Guyer has been more or less a part of a platoon for much of the season. That means that Guyer has enjoyed the platoon advantage -- facing a left-handed pitcher -- in 40% of his plate appearances, while Jennings has only had the advantage in 21% of his.
And lastly, there's the issue of defense. Jennings is very good. You can tell this when you watch him because he's fast and he takes good routes. You can also tell this when you look at UZR statistics because he's now played 1,414 innings in left field at +17.6 runs per 150 games, and 2,356 innings in center field at +1.9 runs per 150 games. Center field is about seven runs more difficult than left field, so that time in left field is approximately equivalent to spending time in center field as a +10 fielder. Put them together, and DJ is somewhere between +2 and +10 runs above average per 150 games in center field. The number may not be precise, but that doesn't matter. The conclusion is that Desmond Jennings is an above average center fielder, and there are only a few people in the world who can make that claim, and even fewer of them who can make it while also hitting at an above average level.
Brandon Guyer has also played well in left field, although his innings are too low for me to cite UZR stats with any confidence whatsoever. The eye test, though, says that he's not quite as fast as Jennings. And because we know just how rare above average major-league center fielders are, the likelihood that Guyer is one, despite not having that reputation in the minors, is small.
So yeah, it's great that Brandon Guyer is succeeding in the majors now that he's finally gotten his shot. He's a good player to have on our team. He's not a replacement for Desmond Jennings, who has stepped into B.J. Upton's shoes brilliantly, as the player most underrated by Rays fans.