When the Pirates won the second most games from 2013-15, the club’s rotation was seventh in all of baseball in starting pitcher strikeout rate. Over the last two seasons, the club has the 20th most wins in baseball and are also 20th in starting pitcher strikeout rate.
It’s no secret that missing bats is important for pitchers. Last season hitters hit .255 with a .426 slugging, and in at bats not ending in a strikeout, hitters hit .336 with a .562 slugging. It’s vital for pitchers to miss bats, it’s the only way to (essentially) guarantee an out. Contact forces additional parts in order for an out to made, a fielder moving, fielding the ball, throwing, and finally throwing it to another player.
To try to prevent a runner from reaching base, the best way is to miss bats and get a strikeout. But it’s important to do it on a plate appearance basis and not a per nine basis. Using a per nine stat for strikeouts, walks, and home runs strips out important context. A batter facing lots of batters an inning but striking out two batters can artificially inflate that number to make is seem they strikeout more batters than they do. For instance, take 2017 Tyler Glasnow and Julio Teheran:
Just by looking at K/9, it would appear as if Glasnow struck out hitters at a higher rate than Teheran, but that stems from the two striking out a similar rate of batters and Glasnow facing 0.61 batters more per inning. For that reason, a rate basis is better and how we should think of how well a pitcher gets strikeouts.
Team wins and starting pitcher strikeout rate
Looking at the strikeout rate from starting pitchers on a team (x-axis) and plotting their wins (y-axis) since 2013 shows a positive relationship between the two, which intuitively makes sense. It’s just a simple model in which team wins=
The equation above is Team Wins=+ 30.825 + 254.471KRate with an R^2=0.303, meaning that strikeout rate explains 30 percent of the variation in team wins. (For those curious, strikeout rate is significant with a T-value of 8.0 and p-value of < 0.0001.) If a team’s rotation strikes out 25 percent of hitters, this projects the team to win 94.4 games. Of course, this is just a simple model and ignores other variables than explain wins, but it gives a simple look at how important it is for starting pitchers to get strikeouts, as there is a positive relationship between starting pitchers strikeout rate and team wins.
Just looking at starts in 2017 where the pitcher stuck out less than the league average rate of 20.6 percent, pitchers gave up 2.16 more runs per nine innings (RA9) compared to when they struck out at least the league average rate:
Getting strikeouts is important in limiting runs, once again intuitive, but it’s nice to have a number to it. Last year, Pirates starters only had 72 games in which they struck out batters at a rate of 20.6 percent or more. When looking at the six division winners from last year, all had more starts where their strikeout rate was higher than the league average than below. Five of the six, with the one being the Cubs, had 100+ games where their starters struck out more batters at a rate higher than the league average.
Starting Pitcher Strikeout Rate and ERA
Looking at pitchers with 100+ innings as a starter, and only their starting numbers, from 2013-17 shows a negative relationship with ERA and strikeout rate with a R^2 of 0.26, with strikeout rate being significant with a p-value <0.0001 and a T-value of -15.4:
Once again, this is intuitive, as missing bats means less base runners and less chances to allow runs. This simple model of ERA = 6.07123-10.4276KRate implies that a 25 percent strikeout rate would produce a 3.46 ERA. This is the one area in which the Pirates starters could benefit, getting more strikeouts, but it’s not as simple as going out and saying we need more strikeouts, so do so.
Chad Kuhl added a curveball last season, and he saw his strikeout rate increase and ERA decrease. In the first two months of the season in 2017, Kuhl struck out just 18.0 percent of hitters and had a 6.02 ERA. However, after adding the hook around the start of June, Kuhl posted an ERA of 3.58 and struck out 22.3 percent of hitters.
But not all pitchers have that stuff that they can translate into strikeouts by just adding a pitch, especially pitchers who sit upper 90s such as Kuhl did. Pitchers like Trevor Williams and Ivan Nova pitch to contact, and that’s fine as backend starters, but this is one of the areas in which the Pirates might be able to capitalize on.
The 2018 Tampa Bay Rays are going to try a grand experiment where they go with a four man rotation with the fifth starter being a “bullpen day.” The club also plans to be more aggressive in pulling starters, which is a way to try to minimize the times through order penalty.
I’ve written previously about how the Pirates should be more aggressive and try their own version of bullpenning. Chad Kuhl knowing that he only has to go four innings could allow him to increase his strikeout rate a tad more, and a full healthy season of Taillon should allow the same, especially if known he only needs to go five or six innings.
The key to all of this comes from Tyler Glasnow, who will start the year in the bullpen, and he can help neutralize the contact inducing Williams and Nova. This spring Glasnow has a 7.31 ERA, but his swing and miss stuff has played better. In 2017, Glasnow had a strikeout rate of 18.4 percent, but this spring he has a 33.8 percent strikeout rate and he is only walking 6.8 percent of hitters. The ERA isn’t where he would like it, but it’s spring training and a focus on process over results is needed.
If Glasnow is able to carry over that swing and miss stuff with control into the regular season, the Pirates would have a multi inning relief ace on their hands. The staff on a whole doesn’t look promising in terms of getting strikeouts, especially with two fifths being contact pitchers. To try to capitalize on that mimicking the Rays and having their own version of bullpenning. Teams that win have starters who strikeout batters at high clips, and to get back to winning, the Pirates either need their starters to take a leap forward in that department or they need to get creative and try to find ways to get their strikeout rates up by limiting starters.
*Numbers from Fangraphs