Why do the Yankees want J.A. Happ back? Because there are few pitchers with a better durability and a more effective fastball.

LAS VEGAS — What was an eight-game gap between the Red Sox and Yankees shrunk in the past 24 hours. New York appeared to be close to signing durable lefthander J.A. Happ, while Boston admitted a coming payroll crunch, which it could address proactively by trading durable righthander Rick Porcello.

New York had held its negotiating line on Nathan Eovaldi and Patrick Corbin—losing out on both starting pitchers for want of another year—but stepped up with a third year to close the deal for Happ, an indication of his importance in the AL East and mostly his reliability. Why would the Yankees commit to paying a starting pitcher through age 38? Here is what they are buying:

1. The most reliable of the three free agent pitchers they considered (and the only one among them without Tommy John surgery).

2. An AL East-proven pitcher who is 13–3 with a 3.34 ERA at Yankee Stadium and Fenway Park.

3. A pitcher with a four-seam fastball that ranks with the one of Justin Verlander.

Huh? Happ and Verlander? It’s true.

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First you must start with why the Yankees would go to a third year on a 36-year-old starting pitcher. As Billy Beane likes to say, “We’re all actuaries” when it comes to general managers forecasting performance over age. And over the past 14 years, only one lefthanded pitcher has thrown even 400 innings (just 133 per year) over his age 36–38 seasons: Andy Pettitte.

What the Yankees see in Happ is a lefthander with a low-effort delivery (though his cross-fire stride borders on extreme), good arm and shoulder health history, and clean arm action. At 6' 5", 205 pounds, with his tall posture and the way he stays behind the baseball, Happ reminds me of Chuck Finley as far as how the ball comes out of his hand. Finley held up very well. He threw 545 innings for the Angels and Indians from ages 36–38, going 36–29 from 1999–2001.

The way in which Happ delivers the baseball is better than the metrics in explaining why he is one of the best four-seam fastball pitchers in the game. His four-seamer averages “just” 92.3 mph, one tick below the major league average. He does have above-average spin rate on the pitch (2,334 rpm), though it’s only slightly above average (2,263), ranking below those of 63 other pitchers.

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So what’s the secret? Happ’s fastball simply gets on hitters. It has good “ride” through the zone. It’s hard to explain, but it’s there in the way hitters react to it. Batters hit .203 against his four-seamer this year, and that’s no fluke. He’s been getting these results for years. Over the past four seasons, only three pitchers have used their four-seam fastball to get more outs than Happ:

Most Outs on Four-Seam Fastballs, 2015–18

Player Outs Max Scherzer 1,243 Justin Verlander 1,173 Kevin Gausman 1,160 J.A. Happ 1,061 Jose Quintana 961

That tells you he can keep throwing the pitch and keep getting results. Now let’s measure how hard it is to square up those four-seamers. If we look at lowest slugging percentage against four-seam fastballs in these past four years – not just the volume of outs – Happ again shows up among the leaders:

Lowest Slugging Percentage vs. Four-Seam Fastballs, 2015-18

Player Slugging PCT. Jacob deGrom .339 Robbie Ray .363 Gio Gonzalez .373 J.A. Happ .385 Justin Verlander .386

And that’s how we get to Happ and Verlander having like fastballs—even though Verlander throws his 95 mph. Over the past four seasons, only Happ and Verlander rank among the leaders in volume and efficiency of their four-seam fastball. It sounds unusual to say the Yankees bought reliability by giving a 36-year-old starting pitcher a three-year contract, but that’s exactly what they did.