The Difference Between Starters and Bench Players

If we take for granted that major-league baseball teams are trying to win and not lose games — and, for the most part, it’s probably fair to take this for granted — we can also take for granted that the players whom they use most often and who appear most frequently in starting lineup sare also the best players rostered by those clubs. Put differently: starters tend to be good, bench players less good. That is not informative analysis. It is fact.

What might be informative, however, is a brief study to determine exactly what makes a good or bad backup. What follows is an attempt at such a study.

To begin, let’s first take a look at production by position from starters. There isn’t a precise way to delineate which players are starters and which players are bench material, as those titles often shift throughout the season. For the purposes of this piece, though, I separated all players into two distinct groups: players with at least 250 plate appearances and players who do not have 250 plate appearances. I categorized those in the former group as starters. The graph below shows how those players tend to perform on offense.

There are a few surprising results. First, third basemen top the list. Given that the position is more difficult to play than an outfield corner or first base, we would expect to see third base somewhere in the middle. The next surprise — at least for me — is the appearance of first base in the middle of the pack. First base is generally associated with the most offense, and we would expect to see it at the top. The final interesting placement is at catcher. That catcher appears last is not a surprise, but that it’s pretty close to average and not too far behind the rest of the up-the-middle defensive positions stands out.

When we discuss relative position strength and the standard of offense deemed acceptable, we do so in terms of overall production at the position. That includes not just the starters, but the bench players as well. Removing the interlopers with under 50 plate appearances at a position, we will classify bench players as those with at least 50 PA and fewer than 250 PA. The graph below shows how those players perform.

This graph appears to reveal a more the traditional view of offensive strength by position. The players getting less playing time at first base are likely only on their respective teams because of their ability with the bat or potentially getting a slight rest from a more rigorous position but having a bat that needs to stay in the lineup. While third-base starters have performed incredibly well this year, the backups have hit more like center fielders and second basemen — just as we would expect. This makes sense, as the backups at second base are often going to be the backups at third base, too. It’s a lot easier to take a guy who can play at second and put him at third with some sacrifice with the bat than to try and take a first baseman and get him to play third. The chart also shows just why catcher is at the bottom of the spectrum when it comes to offense, as backup catchers are often terrible on offense.

The table below shows the differences between starters and bench players this season.

What these numbers seem to indicate is that, having a halfway decent backup in the corner-outfield spots, third base, and catcher could make a pretty big difference compared to average teams. Splitting the difference between the backups and the starters at those four positions for just 200 PA each would be worth a full win over the course of a season over the average team. These numbers are specific to just one season, however, which is how we get anomalies like bench shortstops hitting better than starting shortstops. Javier Baez and Alex Bregman have gotten some time there and hit well. Running those same numbers since 2002 gives us the table below.

Here we see the numbers even out a bit. Nearly all positions feature pretty close to a 20 wRC+ difference between the starters and bench players. Curiously, the shortstop position is the one with the least difference offensively. My hypothesis would be that teams are willing to let decent-hitting second basemen fake it at shortstop from time to time, and add in that teams likely prioritize defense from the position among starters, hence the low starter numbers. Using many years does help smooth out the numbers to provide fairly uniform differences. Using the same math as above, that means that having an above-average backup at any position is going to be worth roughly half a win over an average team even in only 200 plate appearances.

If your team’s backup catcher is awful offensively, you are not alone. It is incredibly difficult to find a decent option once the starters are spoken for. This is true not just because of team preferences, but because of the talent available. I went position-by-position using Steamer’s preseason projections, separating the top-30 hitting players at each position from player Nos. 31-90. Here are the differences by position.

This is just a one-year snapshot, but it does provide some help in showing the distributed talent level by position at the plate. This provides some support for second baseman masquerading as shortstops, as the level of hitters below the starting shortstops is actually really bad. Depth is probably an undervalued and potentially misunderstood concept when it comes to big-league teams. Most players are backups because their level play is quite a bit lower than that produced by the players ahead of them. Teams with good backups — at least offensively, as defense admittedly wasn’t much of a consideration here — can gain a pretty big advantage over their rivals.