What Happens When a Pitch is Thrown: Part 2 - Strikes and Balls

Here is the story behind this series.

In the first entry, we determined that just under 45% of pitches are in the strike zone, and pitchers who get it in the strike zone regularly, particularly those who exceed 46%, do better than those who don't. But I noted that throwing into the strike zone isn't the same as getting a strike, because the umpire can get the call wrong in or out of the zone and the batter may swing at a pitch outside the strike zone. So now we're going to just look at strikes.

How often is a pitch a strike? Per Fangraphs, of the 709,916 pitches thrown last season, 451,242 were strikes. That's 63.6%.

Is there a difference between the leagues? A little bit: 63.4% in the American League, 63.7% in the National League. I'm guessing here, but I assume the difference is due to pitchers batting. We've all seen pitchers flailing away at pitches outside the strike zone.

Is there a difference between starters and relievers? Starters get strikes on 63.7% of pitchers, relievers 63.4%. That surprised me since, as we saw in the last post, relievers throw more pitches in the strike zone. Digging deeper, AL starters and relievers are about the same: 63.4% starters, 63.3% relievers. The larger difference is in the NL: 63.8% starters, 63.4% relievers. Again, I assume that's because starters are more likely to face the other team's pitcher than relievers, who are more likely to face a pinch hitter with better strike zone command

Is there a difference between right-handed and left-handed pitchers? Not enough to care about. It's 63.4% for lefties, 63.5% for righties. 

Does it matter? I broke all pitchers into ten groups, based on the percentage of their pitches that were strikes. The top group, Group 1, had strike percentages between 67.7% (NL Cy Young winner Clayton Kershaw) and 83.3% (the Phillies' John McDonald, who got 10 strikes on the 12 pitches he threw - the most for a guy you've heard of is 73.9% for Boston's closer Koji Uehara). The lowest 10%, Group 10, got strikes on less than 60.5% of their pitches. Here's how the 10 groups fared in terms of ERA, WHIP (walks and hits per inning), and percentage of batters struck out, walked, or allowed a home run:
   Group ERA  WHIP   %K    %BB   %HR
     1  3.16  1.10  22.0   4.8   2.4
     2  3.39  1.17  21.8   6.4   2.5
     3  3.80  1.23  20.3   6.5   2.7
     4  3.52  1.24  20.4   7.1   2.3
     5  3.72  1.25  20.9   7.8   2.7
     6  3.86  1.32  19.0   7.3   2.5
     7  4.00  1.33  19.8   8.4   2.5
     8  4.14  1.39  20.0   9.6   2.5
     9  4.61  1.47  17.4   9.3   2.5
    10  4.64  1.55  16.9  12.3   2.5

This is a lot more dramatic than the chart in the last entry, which divided pitchers by their ability to pitch in the strike zone. Throw out the freak ERA for Group 3 (or, more accurately, blame it on CC Sabathia, Dan Haren, R.A. Dickey, and Joe Blanton), and every successive group is worse than the one before it. Getting strikes is clearly important, the more the better. The top 10, Group 1, has starters like Kershaw, Cliff Lee, David Price, and Jordan Zimmermann, and relievers like Uehara, Mariano, and Kenley Jansen. The best pitchers get the most strikes.

A fair question to ask: Why is getting strikes a bigger determinant of pitching success than getting pitches in the strike zone? Ah, that's where things start to get interesting. Next post.

What We Know So Far: The more strikes a pitcher gets, the better he fares.