Why Yanks chose Severino to start against A's

On Tuesday, the Yankees named Luis Severino their starter for tonight's American League Wild Card Game, opting for their flamethrowing ace over Masahiro Tanaka and J.A. Happ. Amid all the factors New York had to consider before making that choice, one stands strongly in Severino's favor: His stuff against the A's lineup's strengths and weaknesses.
Severino matches up the best of any of New York's starting pitchers against Oakland's hitters, and specifically, he has one key advantage each over Happ and Tanaka.
Here's what tips the scales for Severino over each of his fellow starters.
:: AL Wild Card Game schedule and results ::
Severino vs. Happ: Extreme velocity
Severino has one of the hardest fastballs in the Majors. He averaged 97.6 mph with his four-seamer this season, the fastest of any starting pitcher. High velocity is, of course, an advantage in general. But against the A's in particular, it could be a critical difference-maker.
Highest average fastball velocity among starting pitchers in 2018
Minimum 500 fastballs thrown
1. Luis Severino: 97.6 mph

2. Noah Syndergaard: 97.4 mph
   
3. Nathan Eovaldi: 97.1 mph
   
4. (tie) Gerrit Cole: 96.5 mph
   
5. (tie) Tyler Glasnow: 96.5 mph
   The A's are one of the best hitting teams in baseball against lower-velocity fastballs. But against high velocity -- the kind Severino has -- they've been one of the worst.
   Statcast™ has a metric called expected wOBA -- an overall measure of offensive performance, based on quality of contact made, walks and strikeouts. Against fastballs below 97 mph, the A's had an xwOBA of .391 this season, the second highest of any team behind only the Red Sox (.397). Against fastballs thrown 97 mph or harder, their xwOBA plummeted to .260, the third-worst mark of any team, ahead of only the Giants (.225) and Rays (.245).
   The A's also whiffed on 32.0 percent of their swings against 97-plus mph heat -- the highest whiff rate of any team against fastballs at that speed. Against fastballs under 97 mph, their whiff rate as a team dropped to a much more respectable 17.6 percent, ranking 15th in MLB.
   That's huge when comparing Severino to Happ. An average Severino four-seamer exceeds that 97-mph mark. He had 73 strikeouts this season on 97-plus mph heat, second most of any pitcher behind only Cole's 86. That could spell trouble for the A's.
   Happ averaged 92.3 mph and maxed out at 95.7 with his fastball this season. But he still threw it 58.9 percent of the time, making him one of the top 10 heaviest four-seam users among all regular starting pitchers. That would be a matchup for the A's to exploit.
   Severino vs. Tanaka: Reliance on the chase
   Tanaka is one of the game's craftiest pitchers. Unlike Happ, he throws almost no fastballs at all -- Tanaka's 31-percent fastball usage rate was the lowest among all regular MLB starters in 2018. Instead, Tanaka gets hitters to go after his splitter and slider -- he induced swings on 33.7 percent of pitches outside the strike zone, the fourth-highest chase rate among starters.
   That's great against a free-swinging team, but the A's are patient and disciplined. As a team, they chased only 25 percent of balls outside the zone all year, the second-lowest rate of any offense (the Dodgers ranked first at 23.8 percent).
   
   That means they could neutralize Tanaka's biggest strength. Tanaka is heavily dependent on getting those chase swings: 37.9 percent of the outs he got in the regular season were on pitches outside the strike zone, the ninth-highest figure among starters. But the A's -- their strongest hitters in particular -- rarely chase.
   Key A's hitters who had chase rates lower than MLB average in 2018
   Matt Olson: 21.0 percent
   Matt Chapman: 21.1 percent
   Jed Lowrie: 21.3 percent
   Khris Davis: 23.3 percent
   Marcus Semien: 23.6 percent
   Ramón Laureano: 26.5 percent
   MLB average chase rate: 27.6 percent
   Oakland does a good job forcing pitchers into the strike zone. But even inside the strike zone, Severino can be tough to handle, because his stuff is so electric. And he's much more effective in the zone than Tanaka.

On plate appearances decided on pitches within the zone, Severino allowed a .266 batting average and a .424 slugging percentage in the regular season. Tanaka allowed a .302 average and a .569 slugging -- the eighth-worst in-zone slugging allowed by any regular starter.
There are teams where the best option might be a starting pitcher like Happ, who comes right after hitters with elevated fastballs, or Tanaka, who baffles them with a steady diet of splitters and sliders that dive below the zone. But for the Yankees against the A's in the AL Wild Card Game, it's Severino.