It sounds like an air piston when Alex Len breathes, gasping in sync with the tennis balls being fired at his face. He snatches them quickly and ferociously, exhaling with metronomic rhythm, the sharp pfffs echoing inside this cavernous auxiliary gym on a humid May morning at the University of Maryland.

Len appears almost regal seated upon the stack of red gym mats parked inside the paint. Four trainers and team managers surround him on the perimeter. A fifth stabilizes Len from behind. Stiffening his back, Len throws his hands into the air, ready to catch. Initially, it looks like he is surrendering.

Except this isn’t a surrender. The challenge, after all, has just begun. Since declaring for the NBA draft in mid-April after two seasons with the Terrapins, Len has surrounded himself with a trusted crew, each member tasked with arming the 19-year-old Ukrainian for the next battle.

A third ball gets added to the drill, a blue one no bigger than a softball. He’s getting in a rhythm now. Five in a row. Six in a row. Now a fourth ball, purple and heavier than the rest. It’s constant commotion, but the 7-foot-1 center looks almost peaceful.

It’s almost enough to forget about the silver walking boot strapped around his left foot.

‘He’s a tough kid’

Len had surgery to repair a partial stress fracture in his left ankle on April 27 at Charlotte’s Mercy Hospital. He walks with crutches but hops the stairs, two at a time. The foot’s range of motion has improved, but it still hurts when trainers grab the heel, arch back his toes and apply pressure to stretch it out.

Stress fractures worsen over time, compounded by overuse, so it’s impossible to pinpoint exactly when the injury occurred. Maybe during the ACC tournament in mid-March, when Len says he struggled to walk around the team hotel after games. Maybe against Iowa in the National Invitation Tournament semifinals on April 2, when the pain reached its peak. Right now, though, the origins don’t matter so much.

“What it did show me,” Maryland Coach Mark Turgeon said, “was that he’s a tough kid, a very tough kid who played through it, played through pain, which eventually became an injury. I think Alex was just trying to win as many games as he could down the stretch, and be successful. Never one time did the kid come to me and say he had a really bad injury.”

Once Len decided on surgery, he traveled to North Carolina to see Robert Anderson, a renowned foot and ankle surgeon responsible for operating on several high-profile NBA stars, including Kyrie Irving and Stephen Curry. Len wants NBA teams to be reassured when evaluating his health, and there’s no one more trusted under these circumstances than Anderson.

It was the first major surgery of Len’s life, and his body reacted poorly to the anesthesia, which induced nausea and vomiting. He also doesn’t quite remember posing for a pre-operation photo snapped by his agent, forming a circle with his thumb and pointer finger around his eye, a monocle in full hospital gown.