Coventry boss Mark Robins says he was confused by the decision to book Cyrus Christie for tripping a pitch invader.
A fan ran onto the pitch in their Johnstone's Paint Trophy northern final first leg 3-0 loss to Crewe, and Robins supports the defender's actions.
"He stopped him [the fan] in his tracks and waited for the stewards to remove the supporter," Robins told BBC Coventry & Warwickshire.
"To produce a yellow card for that was strange to say the least."
He added: "He's stopped the fan from running all over the place. He [the fan] had better movements than some of our players today."