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Bud in: to interfere, interject, or meddle, in another's affair with the direct intention to take sides in a dispute or argument.

The term is a variation of the phrase "butt in."
I could see that they had your back up against the wall; so I had no choice but to bud in, on your side of the situation, to make it a fair fight.
by UrsaSolus October 05, 2011