With the scoreline at 1-0 to the Baggies six minutes into the second half, U’s head coach Buckingham was shown a yellow card by referee Leigh Doughty.
The official had just blown for a free kick when Albion skipper Kyle Bartley hit the turf after a mild nudge in the back from Mark Harris, as the Welsh striker looked to get in behind the away defence.
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Buckingham said: “Mark Harris had just gone through and used his body to get over Bartley’s shoulder, and it was more my body language.
“I didn’t say anything, and as the game was on TV, they don’t like to see that side of things because it then provokes the crowd. It wasn’t anything that I said, it was more my action.
“I didn’t think it was a foul, I thought it was a good run and he used his body well to get in. The referee is in charge of the game, he gave it, and I have to accept that.”
Buckingham added: “I apologise for that. The referee is there to referee the game, and they’ve got a hard enough job.
“There were a couple of things that I thought went against us, and I need to keep my emotion in check on the sideline if I’m asking the players to do that.
“I own that one, and it’s down to the referee to make the decisions that he sees fit.”