WATCH: Isner puts unreal amount of backspin on volley vs. Federer

This might be the volley of the tournament, via John Isner.

John Isner hit the volley of the tournament. (USATSI)

John Isner is known for his monster serve. But against Roger Federer on Monday at the 2015 US Open, Isner showed that he's more than just a big server. 

When Federer had a chance to go up a break in the first set, Isner charged the net for a volley. Federer rapidly closed in on the ball, but then he suddenly slowed to a halt. Federer gave up on the ball. 

That's because Isner had put so much backspin on his volley that the ball spun back over the net onto Isner's side of the court.

John Isner epic drop volley that bounces back on his side of the net... In an endless loop. https://t.co/icbcgPrgpl

— Joe (@ProdigyRep) September 8, 2015

And here's a closer look at the spin on that ball.

Spin doctor John Isner wins a cheeky point off the legend #USOpen! https://t.co/kJGGCUVvI6

— Austin Manak (@Cottstigan) September 8, 2015

Isner would hold serve and win the game. The winner of the match will advance to the quarterfinals of the 2015 US Open.