Phillies: Jake Arrieta’s early 2019 success gilded in many fashions
By John Town
Jake Arrieta’s on-field results have been strong so far this year, but Phillies fans shouldn’t expect this to continue much longer.
Upon first glance, Jake Arrieta has pitched very well this season. In three starts he has a 2-1 record, 2.25 ERA, and 1.150 WHIP in 20 innings. His seven-inning, 108 pitch performance Friday night guided the Phillies to a 5-1 victory over the Marlins.
However, the further you look into Arrieta’s numbers, the more issues start to emerge. It doesn’t bode well for a rotation that has had more than its fair share of struggles three and a half weeks into the season.
To begin with, Arrieta is walking a lot of batters. His 12.4% walk rate is 12th-highest among qualified major-league pitchers. Six of his ten walks this year came during his first start on a cold night March 31, which does inflate that rate some.
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Conversely, Arrieta’s strikeout rate is okay but doesn’t jump off the page at 18.5%. For reference, the league-average strikeout rate for pitchers this year is 23.3% and 22.3% last year. Again, this number is weighed down by his one-strikeout, seven-inning performance April 6.
Arrieta picked up eight swinging strikes Friday night but has just 17 altogether this year. His 5.6% swinging strike rate is the lowest among all qualified pitchers this year.
The small amount of swinging strikes leads to the below-average strikeout rate and more contact.
Arrieta has gotten extremely lucky with balls in play as opposing hitters have a batting average on balls in play of just .212. His career batting average on balls in play is .270, and the league average is .289, so some regression will come.
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This low BABIP comes despite hitters generating lots of good contact against Arrieta. His 9.3% soft contact rate is sixth-lowest in the league. Opposing hitters have an average exit velocity of 91.0 mph against him, 37th out of 167 pitchers with 25 or more batted ball events.
All told, hitters should be generating far better results than they are currently against Arrieta. While opposing hitters have a .188 batting average, .294 slugging percentage, and .272 weighted on-base average, they have an expected .264 batting average, expected .484 slugging percentage, and expected .366 weighted on-base average against Arrieta based on their exit velocities and launch angles.
Essentially, Arrieta should be producing far worse than his ERA and WHIP would suggest. His 4.75 fielding-independent pitching, 5.38 expected fielding-independent pitching, and 5.38 skill-interactive ERA are further evidence of this.
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Arrieta has managed to succeed despite what his underlying numbers should suggest, but don’t expect that to last for long. Hopefully, other starters in the rotation can pick up the slack when he inevitably falls back to earth.