By definition, assault is "a physical attack upon". Battery is "1. In criminal law, this is a physical act that results in harmful or offensive contact with another person without that person's consent. 2. In tort law, the intentional causation of harmful or offensive contact with another's person without that person's consent."
There are truly violent acts, clearly without the need for interpretation of intent. Then, there are physical acts that do not result in physical harm, but result personal offense.
Now, here is where it gets a bit nebulous for me,...intent from the person carrying out the act,...interpretation from the person on the receiving end. There are situations where the person carrying out the act might be socially awkward, intending to be somewhat cheeky, a light-hearted physical act (a nudge on the arm or shoulder, a slap on the back or shoulder, etc.). However, it is how that act is being received that is most important. If it appears, out-of-context, a surprise, or the person carrying out the act was not reading the other person correctly,...that is when offense is taken.
When I was in my youth and as a young adult (pre-1990's), these sorts of things were more socially acceptable and common,...physical acts were part of normal communication,...even if interpreted as an offense or rude. Back then, it was the intent that counted, and if you misinterpreted the intent and it resulted in you being emotionally upset,...you were considered weak, immature,...a cry baby. Now-a-days,...quite the opposite.
Obviously, you took offense,...so legally, you are in the right to involve event security and to even take some legal action.