Live-Armed and Dangerous: J.J. Wolf and one the most distinctive, explosive serves in tennis

WATCH: Wolf defeats Tiafoe in the Dallas semifinals

“It’s a lot faster than I thought. It’s like when you hear that loud pop of a baseball when it hits the mitt. Or in tennis, it’s when you’re returning serve and the ball just goes past you and pops into the screen behind the court and you’re like, ‘Damn, that ball was moving a lot faster than I thought.’ You can tell J.J. has that explosiveness.” Brad Gilbert, former elite coach and ESPN analyst, on the blazing serve of 44th-ranked J.J. Wolf

The term “live arm” is a familiar one in sports, most prominently baseball. But defining just what that means is a tough assignment that inevitably takes you deep into the weeds of biomechanics. One thing we do know by the simple evidence of our eyes is that Wolf, while just 6-feet tall, has a serve that stands out from those of his peers, including some prominent big men, in ways that add up to make it one of the most distinctive, explosive shots in tennis.

Wolf brings that elusive “pop,” and it’s an exciting thing to behold.

A 24-year-old righthander from Cincinnati, Wolf has ridden that serve from outside the Top 100 at the end of last July to his current ranking of No. 44. He’s an outstanding athlete from a family choc-a-bloc with them (by his own count, Wolf has some 15 to 20 cousins who have competed in Division I college athletics, including basketball, tennis, volleyball and football), but he’s the only one whose calling card is a blistering serve. Only 12 ATP players hit more than Wolf’s 8.2 aces per match, but his slice second serve is no less menacing.

“I have studied J.J.’s serve and he does a couple of things really well,” Dr. Mark Kovacs, a specialist in tennis biomechanics and training at the eponymous Kovacs Institute, told me recently. He said the elements that make Wolf so explosive are a formidable cocktail composed of a low ball toss, a good use of his back hip (more on that a little later), excellent lower-body explosiveness (without which, Kovacs said, your ceiling as a server is “capped”), and outstanding arm speed.

Kovacs has formally identified eight stages to a tennis serve, and has developed terminology for each. The first two stages are of the most importance. How quickly and forcefully does the back hip drive up from the “loaded” position as a player launches into his serve? Second, how quickly does the arm move from the supinated position, often called the “backscratcher,” through to contact (a process known in both baseball and tennis as “long-axis rotation)?

“Those two components are the main markers for serve speed,” Kovacs said, “If they are working well, that correlates with serve speed.”

The parallels between serving a tennis ball and pitching a baseball are striking, so it should come as no surprise that in his youth Wolf was a promising pitching prospect—until he gave stickball up for the racquet early in his high school years.

“I’ve been told I have a ‘live arm,’ I’ve been told that since my younger years, when I was a pitcher,” Wolf told me recently. “I’ve tried to incorporate some of what I was doing pitching into my tennis, too. I have a couple of slider serves that look like some of my older pitches.”

Wolf went on to compare spot pitchers and speed pitchers, noting that there are parallels in tennis. He also noted that pitchers have a “release point” that is comparable to where a server tosses the ball.

“If you have a bad release on the mound, it becomes a wild pitch,” he said. “In tennis, a bad release ends up a fault.”

Having a low toss is almost de rigueur for a player who wants to exploit a live arm to the maximum. Arm speed is a key to superior serving, but a low toss makes the entire process seem that much faster—never mind the way it can disguise the direction of a serve. It’s no wonder that, as Gilbert said, even an experienced returner facing a live-armed opponent can be taken aback by the speed of a serve.

“I try to hit the ball right at the apex of the toss, I try not to let the ball drop at all,” Wolf said. This calls for greater timing than the more leisurely high toss, along with great muscle memory. And finally, Wolf makes his toss to his right and forward, which makes his slice that much more lethal—and has his mass moving forward into the court.

“It’s like when you throw a baseball,” he said. “If you try to throw it from behind your head it’s not going to go very fast. But if you throw it out to the right it’s kind of natural and it can kind of whip through there real quick.”

Wolf’s modest height puts him on the small side in today’s game. On the other hand, as Kovacs notes, he has exceptional lower-body strength, his quads sometimes lifting him high off the court as he explodes into a serve.

Gilbert doesn’t believe that Wolf’s stature is an issue. He points to the precedent of Johan Kriek, a South African active in the 1970s and ‘80s. He stood just 5-foot-9 but had quads like propane tanks, dazzling racquet-head speed, a superb slice serve, and great quickness. Kriek won two Australian Open titles on grass, and made the quarterfinals or better at nine other Grand Slam events.

If that seems like reaching too far into the past, Nick Kyrgios may be the most prominent example of a contemporary pro with a live arm. He was a finalist at Wimbledon last July, on the surface tailor-made for the explosive, live-armed player. Wolf has yet to play his first ATP match on turf, but the way he serves, it may seem like he’s saving the best for last.