#1 He beat up a heckling fan that decided to step into the ring
There is a line between the wrestlers and the fans. Wrestlers don't put their hands-on the fans sitting in the stands, and fans don't put their hands-on wrestlers or try to come into the ring.
A female WWE star said her life is in danger. Details HERE
If fans make the mistake of coming into the ring, in the wrestlers' mind they are fair game, and thus the invading fan will find themselves in a legitimate fight, likely receiving a legitimate beating because they decided to break the rules.
Before Kevin Owens was who we see today, he competed under his own name of Kevin Steen. On one particular occasion during his time in Montreal, a time when he was still learning his craft, a fan at ringside was vociferously heckling Steen. The situation quickly escalated, and Steen suggested the fan come into the ring.
What happened, however, is a friend of the heckler, who was drunk at the time, decided he would step into the ring. It wasn't a very smart decision, and the consequences were that Steen relentlessly beat the drunk fan up.
Steen has commented on this incident in the past and has never expressed regret for doing what he did. If a fan crosses the line, they run the risk that they could be justifiably harmed.