Starting Pitching Depth and the Arroyo Signing

Before Patrick Corbin got hurt, I wanted to write about—ironically enough—the team’s starting pitching depth. The average team uses ten different starting pitchers over the course of a season. Bronson Arroyo was signed to solidify the rotation. Critics of the Arroyo signing have conceded that he is durable, but commented that he was simply providing league average performance. Sometimes league average performance isn’t so bad. This is one of those instances.

Eno Sarris over at FanGraphs wrote a great article tabulating the odds of injuries to a team’s rotation, drawing from Jeff Sullivan’s research. They calculated that any given team’s starting pitchers average 360 days on the DL in six trips. But as Sarris points out, this is skewed by people who spend the entire year on the DL (see Corbin, Patrick).

Even if the team only suffers four 60-DL stints, they will only have the opening day rotation 22% of the time. This means that a sixth pitcher is being used 78% of the time. On average, teams will need a seventh starter for 22% of the season–or about six starts. And then an eighth starter will be needed for about 4% of the time—six games a season. Ninth and tenth starters are generally used sparingly.

If Arroyo hadn’t been signed and Corbin was out, the rotation would include Wade Miley, Trevor Cahill, Brandon McCarthy, and Randall Delgado. The fifth starter would be someone like Archie Bradley, Josh Collmenter, Bo Schultz, Zeke Spruill, Chase Anderson, Andrew Chafin or Charles Brewer. If Bradley opened the season with the team, he would be a free agent one year earlier. (I talked about the logistics of that situation last week.) Collmenter could start, but the team seems to like him in long relief. Or, one of the other pitchers could start the season in the rotation. None of those guys have proven themselves at the major league level—it’s unlikely that they would have provided average production. And, as the research above shows, at least two and most likely three of these pitchers would have to start multiple major league games. That would have been worse. Anyone not named Archie Bradley on that list is far from a sure thing.

With Arroyo in the fold, Delgado becomes the fifth piece to the rotation. Then it seems much easier to keep Bradley in triple-A. We’re getting 35 starts from Arroyo instead of 35 starts from what would likely be some combination of Schultz/Spruill/Anderson/Chafin/Brewer, at least to start the season. Basically, Arroyo pushes everyone else down a rung, from sixth starter to seventh, or from seventh to eighth.

But even without a Corbin injury, the Arroyo signing would have been fine. Delgado would have been the sixth starter, allowing the rest of the pitchers fight for a seventh spot. Delgado is better than all of those pitchers with the exception of Archie. But you don’t want to have to lean heavily on your young arms. In this scenario, Delgado would have had a lighter load, and Archie would not have to be rushed. As we’ve seen recently, young arms are fragile. If the Arroyo signing helped keep Bradley out of harm’s way, then I’m all for it.