Although he led with his arm, Defoe kept his eyes on the ball at all times.
"I've not seen a replay but the boys looked at it at half-time and they all felt it was harsh," Redknapp said.
"They said Jermain didn't take his eye off the ball and he's not an aggressive player anyway.
"To be fair, at times I wish he was more aggressive in games away from home - not in a nasty way - but he's not the type to do that."
Asked if he would appeal against the decision, Redknapp did not give a direct answer, although he implied he would not.
"He'll be a big miss for us, but we're lucky because we've (Roman) Pavlyuchenko and (Peter) Crouch, and we've two home games coming up, so we're not so badly off," he added.