I watched that video you posted. You are making huge leaps in logic to get to a point where you can definitively claim that they were there "looking for trouble" (which is a dogwhistle phrase if I've ever heard one).
The whole point of a protest is to go to a place where your opposition will be visible. It would be illogical to protest in a place where you cannot be seen or heard. So, for non-Trump supporters, protesting at a Trump rally makes sense, and is perfectly legal. In that video, I saw a Trump supporter grab the sign of a protestor and rip it up before the protestor advanced and shoved the Trump supporter (0:08), I saw a white man with a camo hat and American flag draped around his shoulders (who I am going to go ahead and say is a Trump supporter) and a black man (who I will say is a protestor) fighting, but no inciting incident to be seen (0:12), and I saw a Trump supporter screaming into the fact of a protestor, and when the protestor backed up the Trump supporter advanced and continued screaming in his face before the protestor threw a punch (0:18).
Now, you can make all the leaps in logic you want, but just by watching the video, it shows two instances of a Trump supporter either trying to prevent the opposition's right to free speech (ripping up the sign) or shouting down a protestor to prevent them from exercising free speech (the guy screaming in a protestor's face). The other instance of a scuffle was neutral in the video as you could not see an inciting incident. So, in my eyes, the Trump supporters were the ones trying to prevent the opposition's free speech, not the protestors, and it definitely appeared that the Trump supporters were inviting violence because they could play snowflake and pin it on the protestors.