Velocity is only one piece of the pitching puzzle, but it’s an important one.

Fastballs (specifically, four-seamers and two-seamers/sinkers) continue to get faster across the sport. They reached a record average of 93.1 mph in 2019, including 92.6 mph for starters, according to Statcast.

When starters threw fastballs below 92 mph in 2019, batters hit .307 and slugged .561 -- meaning they were collectively, more or less, J.D. Martinez. Between 92-95 mph, that dropped to .272/.469. And when starters cracked 95 mph, opponents hit only .241 and slugged .396.

There is so much more to it, of course. Breaking ball usage continues to climb. And even when it comes to fastballs specifically, velocity does not account for location, spin, movement or deception. So high velocity is not required to have success. Just ask Zack Greinke, Kyle Hendricks, Hyun-Jin Ryu or many others.

Still, it’s worth looking at which starting rotations are set to turn up the heat the most in 2020. To do this, MLB.com looked at each team’s projected starting five, combined with innings projections from FanGraphs. For each pitcher, 2019 average fastball velocity*, per Statcast, was factored in, and this was weighted for playing time by considering each pitcher’s projected innings and 2019 rate of fastballs thrown per inning.

*Only a pitcher’s average fastball velocity as a starter was used. Pitchers who missed all of last year were assigned their 2018 velocity. Those who pitched only in relief last year had their 2019 average discounted by 1 mph to account, roughly, for a typical velocity drop between those roles. For pitchers who have yet to appear in MLB, velocity was estimated based on scouting reports.

Most teams use far more than five starters to get through a season, so the inevitable additions and subtractions will affect this list as the season goes along. But based on how things are shaping up heading into Spring Training, here are MLB’s 10 hardest-throwing rotations.

1) Rays: 94.9 mph
Hardest thrower: Tyler Glasnow (96.9 mph)
Only Mets starters threw harder than Rays starters last season, though in the latter case, that is not always a meaningful term due to the team’s use of openers and bullpen games. But Glasnow, Blake Snell and Charlie Morton (even at age 36) are all hard throwers, and Tampa Bay will look for far more than the 167 2/3 combined innings it got from Glasnow and Snell in 2019. The 6-foot-8 Glasnow has some of the best stuff in the game, and Snell (95.5 mph), the 2018 American League Cy Young Award winner, has been MLB’s hardest-throwing lefty starter.

2) Yankees: 94.8 mph
Hardest thrower: Gerrit Cole (97.1 mph)
The Yankees dropped from first to second on this list with last week’s news that James Paxton (95.4 mph) will be out 3-4 months after undergoing spinal surgery, a setback that slashed his projected innings total. But they still fare quite well, as Cole’s jump from Houston to New York on a record-breaking contract shook up this list. The projected return of Luis Severino to a full-time role after an injury-marred season also makes a big difference here, and the impact would be even greater if Severino rediscovers his velocity from 2018 (97.6), when he ranked No. 1 among regular starters. Jordan Montgomery replacing Paxton in the rotation would bump the Yankeees down a bit further, although the club also has high-velocity options in Luis Cessa and Jonathan Loaisiga, among others. Domingo Germán (93.9 mph) also is expected to return from suspension in June.

3) Mets: 94.4 mph
Hardest thrower: Noah Syndergaard (97.6 mph)
It remains to be seen how much losing Zack Wheeler to free agency will hurt the Mets on the field, but it certainly dinged them a bit here. His replacement, Rick Porcello (90.4 mph) doesn’t bring nearly as much heat. High velocity is only one of many reasons Jacob deGrom (96.9 mph) has captured back-to-back National League Cy Young Awards. Despite the fact that no starter last year threw harder than Syndergaard, opponents hit .292 against his fastballs.

4) Reds: 94.3 mph
Hardest thrower: Luis Castillo (96.4 mph)
Despite the number above, Castillo’s fastball was not the driving force behind his excellent 2019, at least not directly. That was his spectacular changeup, which produced a .128 opponent average and racked up 155 strikeouts. A full season of Trevor Bauer (94.5 mph) will help the Reds’ velocity further, although the one offseason addition here was soft-tossing lefty Wade Miley (90.4 mph).

5) Rockies: 94.2 mph
Hardest thrower: Jon Gray (96.0 mph)
Coming off a highly promising 2018, last season was mostly a rough one for the Rockies’ rotation -- even on a park-adjusted basis, their ERA was seventh highest in MLB. But there are some live arms here. Unlike most of his colleagues, Gray took a step forward in 2019. German Márquez, Antonio Senzatela and Jeff Hoffman (if he can snag a spot) all average around 94 mph or higher.

6) Phillies: 94.0 mph
Hardest thrower: Zack Wheeler (96.7 mph)
Philly got below-average velocity from its starters a year ago, but that was dragged down by the acquisition of Jason Vargas. He’s out, and in comes Wheeler, the club’s big free agent signing, who last year ranked fifth among starters in average velocity (minimum 500 fastballs). But it’s not just him. Aaron Nola, Zach Eflin, Jake Arrieta, Vince Velasquez and Nick Pivetta all averaged better than 92 mph last year.

7) Indians: 93.9 mph
Hardest thrower: Mike Clevinger (95.4 mph)
There’s been some turnover here, with Clevinger and Shane Bieber (93.1 mph) stepping up for the departed Bauer and Corey Kluber. Clevinger’s emergence as a top-tier pitcher has coincided with his concerted development of more velocity -- up from 92.5 mph over the past three seasons. Note that Cleveland would move down a bit if Adam Plutko (91.1 mph) wins a spot over Aaron Civale (92.6) or Zach Plesac (93.9).

8) Red Sox: 93.6 mph
Hardest thrower: Nathan Eovaldi (97.3 mph)
Replacing Porcello with Martin Perez (93.9 mph) helps, but there are a few major questions looming here. How much will Eovaldi pitch, after injuries limited him to 67 2/3 innings last year, split between rotation and bullpen? Can Chris Sale (93.1 mph) stay healthy, and perhaps even regain his 1.7 mph of lost velocity from 2018? Who replaces David Price, now that he's been traded? (For this exercise, it was Matt Hall, who has never started an MLB game).

9) Athletics: 93.3 mph
Hardest thrower: Frankie Montas (96.5 mph)
This would be a massive leap up the list for Oakland, which ranked 26th in starter velocity a year ago (91.9 mph). That’s partly about more innings from Montas, who lost half of 2019 to a PED suspension, as well as the departures of Brett Anderson and others. But the biggest push comes from a pair of hard-throwing young lefties, A.J. Puk and Jesus Luzardo, who both should get a chance to start in ‘20. They only pitched out of the bullpen in the Majors last season, so their impressive velocities (97.1 and 96.3 mph, respectively) were each adjusted for the change in role.

10) Dodgers: 93.2 mph
Hardest thrower: Walker Buehler (96.5 mph)
Over the years, Clayton Kershaw has seen his velocity slide from the mid-90s to a career-low 90.3 mph in 2019, with an accompanying drop in fastball usage. But the Dodgers still have hard throwers, led by the electric Buehler. The additions of David Price and Alex Wood and losses of Hyun-Jin Ryu, Kenta Maeda and Rich Hill don’t move the needle much collectively, but a bigger role for 23-year-old lefty Julio Urías (94.9 mph) does. If other young arms such as Dustin May (95.5 mph) ultimately grab more starts, that will provide a further boost.