Sheva's headbutt

Sheva should have gotten a red card but the linesman was standing right in front of them if he really really did something that was even out of line he could have seen that perhaps the linesman noticed that is was both of their fault and sheva didn't intend to coz I actually doubt he really did it on purpose, (in the way of I'm gonna walk tho that butcher and headbut him...)
coz the way he did it really laks technique IMHO
nevertheless I you see it in a summary it's very strange indeed that he didn't get a red card. during half time they played that scene again, so the inter fans could see the player that should of gotten a red card scored against them adding to their frustration...
I understand inter fans got really pissed of but the way they expressed their anger ain't gonna help their club...