Martin Ling admitted his tactical errors let his Torquay side down in a 1-0 defeat at Bradford.
Bantams defender Andrew Davies was shown the red card by Hull referee Carl Boyeson following a 24th-minute challenge on Gulls midfielder Danny Stevens.
However, former Hull striker Craig Fagan scored in the 38th minute to secure victory - his first goal in his third league match for Bradford.
Ling, whose team have now gone six games without a win, said: "We didn't work their keeper enough, and my second-half substitutions did not prove effective.
"We knew Bradford's tall defender Luke Oliver was a threat at set pieces. We had the chance to clear the danger, but we didn't, and Fagan scored the winning goal.
"The sending-off seemed to galvanise Bradford. I brought off Joe Oastler because he was on a booking and I thought the referee was looking to level things up."