the grunter shouldn't be allowed to grunt in the first place... not necessary and distracting.

WTF?!? How exactly does he determine it's 'mocking' and not his own grunt at a hard swing?
That's some ol BS right there. If one can grunt, the other can grunt back. If grunting is a problem, guy in blue should lose.
No wonder these judges get hit with tennis racquets.

The ref apparently called hindrance. The USTA defines hindrance as being hindered in playing the point by an opponent's deliberate act. I think one could reasonably argue that the opponent's scream--mocking or not--was a deliberate act that hindered the other player.
http://ftw.usatoday.com/2016/06/tennis-grunts-robin-haase-gonzalo-lama-imitation-penalty

https://tennis-column.blogspot.com/2011/09/hindrance-rule.html

Hah tennis...so archaic.

Oh grunting man. Grunting man, will you ever cease your grunted proclamation of full body, mind, and soul dedication to each swing of the game of tennis?

During sex grunting man exclaims EAUUUGH EAUUUGH EUGH EEAAAAAAUUUUUUUUUGGGHH with the windows down and everyone in the neighborhood sorta liked it at first but now it's just goddamn annoying. Seriously every time, grunting man?

Damn grunting man. Ahhhh grunting man.

What are you grunting at this time? What are you trying to tell me, boy? Timmy fell down a giant gaping anus filled with sores and fissures? Is that why you grunt every time you swing your racket?

No, no, no -- he was just lifting a bag of grain to carry from the mill down to the grainery. Why grunting man has made a name for himself all over the realm (mostly as grunting man). I remember when he was a wee lad, grunting at anything that moved. Birds, signposts, bidets...

What was I saying? Ahhh... GRUNT GRUNT --

Grunting man to the rescue! Hooray Hooray! He comes to save the daaaaaaayyyyyyyyyyy!

Well, in that case, wouldn't topspin or backspin also be a deliberate act that hinders the opposing player?

In fact, I think hitting the ball is just a form of opposing the other player's win. Judges must stop this travesty of competition!

Come on, maybe he was just trying it out to see if it worked or not!