York City boss Lee Mills described his team's defending during the 4-0 defeat to Coventry City as "Schoolboy Errors".
Speaking to Dave Flett of the York Press, Mills, whose team were doing well against the Sky Blues until the former City Reserve team boss decided to bring on PFA Chairman Clarke Carlisle as a 51st minute substitute, said: "The first three goals were ridiculous and I couldn't believe what I was watching. The decision making was diabolical and it was simple schoolboy stuff.
"We won't win any matches playing like that. We put goals on a plate for them and that's the end of us in the competition which hurts.
"I don't know why Clarke did what he did for the first goal. You'd have to ask him.
"You cannot take risks like we did and I don't tell my defenders to do that. I'm gobsmacked by the second half and its my job to address that.
"It's possibly my worst defeat as manager of this football club and it will happen again if we give the ball to the opposition like that and let them put it in our net."