Two late goals from Aiden McGeady and Max Power sealed all three points for the Black Cats.
And Robinson was fuming with that referee Trevor Kettle had not spotted the apparent headbutt.
“We’re waiting for the police to come,” Robinson revealed after the match. “My goalkeeper [Jack Stevens] was headbutted at half-time.
“It’s not right of me to give names.
He added: “There was a bit of a melee.
“Something was said and Jack’s walked behind somebody, he’s just turned around, grabbed him and headbutted him.
“We’ll be waiting to see where this goes from here legally.”
“No Oxford fan would criticise him for throwing his body to try and get something out of it.
“I’m proud of how my players fought for each other, afterwards and at half-time.”