"He that wrestles with us strengthens our nerves and sharpens our skill.
Our antagonist is our helper. "

   – Edmund Burke

Wrestling is an important skill mainly for mages as it prevents them from having their concentration disturbed while casting a spell.  Note however that it only works for melee attacks.  Your concentration WILL ALWAYS be disturbed by any offensive spell casted against you.  At GM level wrestling, you will continue casting at least 50% of the time when under melee type attack.  As wrestling is a combat skill, you will also gain anatomy and tactics skills while training wrestling.  If you do not need or wish for those skills, make sure you lock them.  Wrestling can also be used to disarm an opponent. With anatomy, you will be able to stun punch your ennemy, quite a powerful move in PvP.

Note that since Publish 16, the combination of evaluate intelligence and anatomy works just like wrestling to prevent your concentration from being disrupted. So if you acquired wrestling for that sole purpose, you might reconsider. However, you cannot perform any of the special attacks without wrestling.

Every time you're fighting bare handed, you will stand a chance to gain wrestling.  As every other melee skill, your gains will be difficulty based, so you will need to find an opponent of difficulty similar to your skills. The more often you hit, the more you will gain, so you will need the highest dex possible to hit as often as possible so I suggest having quite a few greater agility potions or regs to increase your dex during your training sessions.

Skill	What to fight
0	Buy Skills from NPC fighter
30	Bulls, Cows, Great Harts, Hinds
40	Skeletons
70	Earth Elementals , Air Elementals
90	Dull Copper Elemental, Rotting Corpses
100	Rotting Corpses

In the 90s, you can higher a fighter at the Jhelom pit.  Just make sure they don't have a weapon.  Shield is alright, but weapon will have you dead in no time.  

Disarming

The most common type of character using this skill are Disarm Mages.

To disarm, you will need 80 wrestling.  You will then have to set a macro in your options.  You have to be close to your opponent to disarm him, so be prepared to sustain damage if you fail.  When you succeed, your ennemy's weapon will be ripped out of his hands and dropped into his pack.  The good thing about it is that it generally takes them a few seconds to realize they are weaponless, enough for you to finish them off before they have time to rearm.

Stun Punch

Combine with anatomy, the stun punch is a very powerful move for mages in PvP. When performed successfully, it temporarily paralyzes your opponent for about 4 seconds, ie long enough for you to cast another combo and finish him off. The beauty of stun punches is that unlike any other form of paralysis, trapped pouches will not break it. Nothing will break the paralysis of stun punches and while paralyzed, your opponent cannot cast spells and cannot run, even if you are hitting him the whole time he's paralyzed