Lefties Galore in the D-backs Bullpen: Is Current Usage Optimal?

It’s been a while since I argued that Will Harris should be treated as the second lefty in the bullpen, someone who could pitch a whole inning with multiple left-handed batters due up while Joe Thatcher could be saved for matchups. When the team broke camp with an unusual thirteen-man pitching staff, the team had not one, but three lefties. So how have Thatcher, Oliver Perez, and Ryan Rowland-Smith been deployed in the season’s first 17 games?

Unfortunately, there have been relatively few games in which the D-backs had a late lead, so we may not yet have a full picture of the team’s real plans. We do have enough, however, for the picture to become clearer; each of the three pitchers have appeared in at least six games. First, a quick check on how they’re actually doing:

This is something of an ode to small sample sizes, and I’m not basing any of this analysis on any of these numbers. But the table is also something of an ode to “it’s better to be lucky than good,” as, in the abstract, it appears that Ryan Rowland-Smith has been pitching best, but doesn’t have much to show for it. This is also a lesson in the fact that the ERAs of matchup guys like Thatcher can be artificially deflated by the fact that they rarely pitch full innings. Even if Thatcher pitched to the same handedness mix (so far, it’s 11 RHH, 12 LHH), his ERA would almost certainly rise if he were pitching full innings.

Why does being deployed as a matchups guy deflate ERA? There are two reasons. One is actually quite small: the benefit of having more runners on base. More runners on base means more ways to get guys out, in addition to more potential outs. You can’t get two outs with a single pitch if you start a clean inning, and mid-at-bat events like pickoffs and caught stealings are credited to the pitcher on the mound.

The second reason is actually pretty significant, though. First outs count more. If I were brought in to face one batter to start an inning and walked him, he’d be on first base with no outs — a situation in which at least one run will score about 44% of the time. If I were brought in to face a batter with no one on base, but one out already recorded, that changes. Suddenly, a walk would mean that at least one run would score less than 29% of the time. It’s a lot like if baseball only had a lesser number of outs per inning — switching from three outs to two outs wouldn’t decrease runs scored by just one-third. It would decrease the average number of runs per inning from .544 to .291 (almost half). If baseball had just one out per inning, the average number of runs scored per inning would drop all the way to .112 (about one per game!).

That’s a long way of saying: ERA isn’t always a terrible way to get at a pitcher’s worth, but, depending on usage, it could be wildly misleading for relief pitchers.

So how have the three lefties been used? Let’s look at two things: LHH/RHH mix, and when they were brought into games.

Right off the bat, it’s clear that Thatcher has been deployed against lefties with more precision (48% of TBF) than Perez (34%) or Rowland-Smith (36%). In fact, the average percentage of plate appearances taken by lefties is 43% (up significantly from earlier eras of baseball). In other words, it doesn’t look like the deployments of Perez or Rowland-Smith have favored left-handed hitters at all.

It’s still early, and despite having a 13-man staff to play with, the struggles of the D-backs rotation haven’t left much room for Kirk Gibson to play matchups. Even Joe Thatcher has mostly been used for longer outings — his first four appearances were for at least four batters or one whole inning, and in one particularly ugly example, he was left out to rot on April 4 despite letting up three hits. Conversely, Oliver Perez was used as a matchup guy in one short stint in Australia and again on April 3, but he faced at least three batters in his other six appearances, including seven batters in two full innings last night. Rowland-Smith hasn’t pitched less than an inning in any of his six appearances.

Here’s how the three relievers were deployed in the games since returning from Australia. Skip down to the bottom if you’d rather not go through the whole review.

On March 31, Perez came in during the 7th with a runner on second and two outs in a tight game. Due up were a switch hitter, a lefty, and another switch hitter. He ended up facing all three of those hitters, but without recording an out.

On  April 2, Thatcher took the ball to open the 7th. Due up were a switch hitter, the pitcher, and then switch, lefty, switch. Thatcher ended up facing all five of those hitters. Rowland-Smith took the ball for the ninth, facing two lefties, a switch hitter, a right-handed pinch hitter and then another switch hitter.

On April 3, it was Perez’s turn: he entered the game in the fifth with one out to face a lefty and a switch hitter, which he did. Rowland-Smith faced a lefty in the eighth and stayed in to face another lefty and a switch hitter before getting lifted in favor of Brad Ziegler for the final out.

On April 4 in what had become a complete blowout by the Rockies, Thatcher handled the entire sixth inning, facing six batters that alternated left-right-left-right-left-right. Perez came in to handle the entire eighth: four righties, a lefty, and a right-handed pinch hitter.

On April 5, Rowland-Smith handled the whole bottom of the seventh, four batters that alternated right-left-right-left. When the #hyphenator entered the game, the Rockies were up just 6 to 4.

In San Francisco on April 8, Rowland-Smith came on in the fourth inning in relief of Trevor Cahill, with two outs and a runner on first. He faced lefty Brandon Belt to end the inning, but stayed in for the fifth in what was still a close game (5-2) to face a switch hitter, three righties in a row, a lefty, and a right-handed pinch hitter before striking out Tim Hudson to end the inning. Oliver Perez came in to handle the sixth: switch, lefty, switch.

Perez repeated the same performance on April 10 to face the same three batters in the same sequence, this time entering in the fourth to face a switch hitter, and, after getting a double play, staying in for the fifth, but just to face a lefty and another switch hitter. Thatcher came in to pitch the entire fifth inning in what was then a tie game, facing a lefty, a right-handed pinch hitter, a righty, and the switch-lefty-switch sequence that Perez had handled earlier.

On April 11, Rowland-Smith pitched the ninth in what was already a lost game (down 0-6). He faced a righty, a lefty, and a relief pitcher.

On the 12th, Perez took over for Wade Miley to open the sixth, facing a righty, the pitcher, and three more righties. He did stay in for the first batter of the seventh: lefty Adrian Gonzalez. In the following inning, Gonzalez came up with the bases loaded and three outs, and Thatcher came in just to face Gonzalez (striking him out).

Thatcher also handled Gonzalez duties (but just Gonzalez duties) on the 13th, striking him out with two runners to close out the sixth.

On April 14, Rowland-Smith handled all of the eighth and ninth innings, entering when the D-backs were down just three runs. He went right, switch, left, right, right, and left to retire the Mets in the eighth, staying on to go left, left, right, right in the ninth in what was clearly a long relief role after Josh Collmenter and Mike Bolsinger had already pitched.

As for the 15th — that was a well-pitched game, other than Bronson Arroyo‘s appearance in innings 1-4. Oliver Perez faced seven batters to get six outs in the sixth and seventh innings in the blowout: left-right-left-right-left-right-left.

The lessons here? Again, the D-backs have not really had the luxury of playing matchups when so far behind. They still used Thatcher in that role last weekend against the Dodgers, though. It seems that the D-backs are aware that Oliver Perez isn’t so much of a matchups guy, but Rowland-Smith has also been used exclusively in longer stints over the last two weeks.

As for optimizing the three pitchers’ use, despite his arm angle and reputation, Joe Thatcher hasn’t been much more effective against lefties (.276) than righties (.307) in his career. I’m sure this is due, in part, to frequently facing one of the opposing team’s best lefty hitters — the hitting skill of the righties Thatcher faces is probably quite a bit lower than that of the lefties he faces.  Neither of the other pitchers are particularly useful as lefty matchup guys, though. Perez was slightly more effective against lefties in 2013 (.304 vs. LHH, .335 vs. RHH), but had a strong reverse split in an abbreviated 2012 (.203 vs. LHH, .302 vs. RHH), and has enjoyed only a slight advantage against lefties in his career (.307 vs. LHH, .344 vs. RHH). Based on his usage, it seems that the D-backs are keenly aware of that. As for Rowland-Smith… it seems appropriate to just use him as if he were a right handed pitcher, given a career split in the majors of .351 against lefties and .340 against righties. And since most of his major league innings have come as a starter, we can’t even assume that he faced better-than-normal competition from LHH.

What do you think? With both Perez and Rowland-Smith not particularly useful against lefties, it seems like there may not be room for both when Cody Ross is able to rejoin the team. And, unfortunately for the Hyphenator, with Perez on a two-year deal, Rowland-Smith may need to be excellent from here on out to keep his spot. That’s the risk one runs with veteran bullpens — inflexibility that leads to inferior results.