Jon Super/AP

Wayne Rooney gave Manchester United an early lead over Liverpool at Old Trafford after just 12 minutes, but Liverpool fans were rightly outraged when a Juan Mata header from an offside position in the 40th minute was allowed to stand, leaving Liverpool with a 2-0 deficit just before halftime.

Ashley Young swung a cross into the penalty area, and Robin van Persie got the slightest of touches to redirect the ball to Mata, who was sprinting to the far post behind the Liverpool defense. When the ball grazed van Persie’s head, Mata was clearly offside — but the linesman missed the call. credited the the assist on the goal

It was difficult to tell if van Persie touched the ball at full speed, but he was credited the the assist on the goal.