<human>: NJ: On a afternoon at a fenced in dog park, my friend witnessed an aggressive dog (let's call it a terrier) getting into it with another dog. Several dog owners began yelling at The terriers owner, to please leash the dog, and remove the dog from the premises, as per park rules. Owner argued with all witnesses, prior to making a half assed attempt to remove the dog. At this time, the collar slipped off.

My friend proceeded to grab aggressive dog by the scruff (in a non-aggressive manner). By doing so, friend managed to break up developing dogfight. 

At this time, the terriers owner spear tackled my friend, pinning them to the floor, and contact was exchanged. 

Police arrived once the fight was broken up, and spoke to the parties involved. Friend presses assault charges on terrier owner. 

Plenty of witnesses to support my friend being assaulted, but now the terrier owner has filed a counter-charge (not sure of proper term)

Could you distill the essence of the text into 1-3 sentences?
<bot>: Friend got tackled and pressed chargers. Defendant is now counter charging. Witnesses in the dozens, all agree to show to hearing.