The 28-year-old today starts a three-game ban after his appeal against a charge which related to a clash between the pair during last weekend’s 2-0 defeat to Manchester City.
Slow motion television replays showed phlegm emanating from Boyd’s mouth that landed on Hart but Bruce insists this was a warped version of what happened.
He said: “You can see on the videos that a bit of saliva comes out of his mouth. But that is not deliberately spitting at someone.
“He is shouting at him. When you look at it, he called Joe Hart a ‘p****’. We have proved it with people who can lip-read.
“When you analyse it, a tiny little bit of saliva comes out. When you spit at someone, it is more ferocious than that.”
Boyd will miss today’s visit of West Bromwich plus Wednesday’s trip to West Ham and the visit to Stoke a week today.
Bruce added: “I will defend him to the hilt. I have managed 15 years and he’s easy to manage. He is low-maintenance. He is a great lad who has come from non-league six years ago. He is not capable of spitting in somebody’s face. It is not George Boyd.
“He is horrified with the charge, genuinely horrified. If there was anything he could do legally, he would.”