The Myth Of Defensive Diminishing Returns
This was written before the Kotchman deal became public. I published it, then took it down when the Gutierrez news broke (so it wouldn’t get lost in the shuffle). This is not written to justify the Kotchman acquisition, which I’m lukewarm about. But it’s still true.
One of the popular phrases you’ll hear people spout is that the M’s “have enough” defense and now need to focus on adding some offense. The idea behind this is that adding another good defensive player will have less of an impact on the team’s overall record, because they are already a good defensive team. This is basically the theory of diminishing returns, where the next unit of something is worth less than the prior unit you acquired.
There are a lot of areas where diminishing returns are an important concept to understand. When stores try to up-sell you into an 84 ounce drink because its the best “value”, diminishing returns helps you realize that the actual value of the liquid beyond what you should consume is actually zero, so you’re paying for something you simply don’t need, and in reality, you should just order the human sized version.
This even applies in roster construction for baseball teams. The Mariners have four power right-handed relief pitchers on the roster right now, with David Aardsma, Mark Lowe, Brandon League, and Shawn Kelley. The marginal value of adding another reliever to the bullpen is diminished from their true talent level, because there are only so many high leverage innings to go around. If the team signed a guy like Jose Valverde, his innings would come at the expense of one of the relievers already here, so the actual value they’d get from Valverde would be less than what he would add to a team with a more shallow bullpen.
Since this is a valid theory, and it works in other parts of roster construction, a lot of people have no problem transferring it over to the defensive side of the game. The assumption is made that a quality defensive team will face diminishing returns from adding another quality defensive player, resulting in a value add that is less than the player’s actual abilities.
This assumption is wrong.
Put simply, almost every single ball in play that matters is only catchable by one player. On a line drive to left field, the quality of the defender at second base is completely irrelevant. That the team already has Franklin Gutierrez and Jack Wilson doesn’t matter when the hitter smashes a line drive down the first base line – the only variable on the defensive side is the quality of the first baseman. If he’s lousy, then the play isn’t getting made, regardless of how good his teammates are defensively.
Now, I know there are plays where two defenders converge on the ball, but those balls in play are going to be outs 99.9 percent of the time even if the second guy doesn’t get there. Even the worst defensive teams in baseball turn 65% of their balls in play into outs. Nearly two-thirds of all non-HR contact is fairly routine for the defense, and those plays are going to be outs whether you have Adam Dunn or Endy Chavez playing defense.
The plays that matter, though, where the runs are saved and wins are earned, are on balls that are smoked. Hot shots up the middle, sinking liners in the gap – this is where the difference in defensive ability comes into play, and on nearly all of those types of plays, there is only one guy who has a chance to convert the out. His defensive quality matters, and that’s it.
History has shown this to be true. When you put a good defensive SS next to a good defensive 3B, their individual numbers do not take a significant hit. Ichiro’s UZR did not go down when the Mariners replaced Jeremy Reed with Franklin Gutierrez, despite Death To Flying Things covering more ground than any outfielder in baseball. Adrian Beltre’s UZR didn’t crash when the team went from Yuniesky Betancourt to Ronny Cedeno and then to Jack Wilson. There just aren’t enough plays that matter where two guys both can convert the out for there to be significant diminishing returns in playing quality defenders side by side.
If the Mariners add a good defensive first baseman, they will get the full value from his glove, regardless of the fact that they already have good defenders around the field. If they upgrade their second base defense, it will improve the run prevention, even though they already have Jack Wilson playing shortstop. There is no evidence that there are significant diminishing returns from adding another good defender to a team that already plays good defense.
Run difference matters. Whether you create another 20 runs with an offensive first baseman or save another 20 runs with a defensive first baseman doesn’t matter. 20 runs are 20 runs, and those 20 defensive runs saved are not dependent on the skills of the other guys on the field.
Now, it’s certainly easier to find a +20 hitter than a +20 fielder at first base, so there’s a pretty solid argument to be made that the team will likely add a guy who is more of an offensive player at the position, but don’t buy into the hype that the team “needs a hitter and already has enough defense”. It’s not true.