Sterling was not the designated Chelsea penalty taker, with Cole Palmer taking spot kicks this season.
"What on Earth is going on there? Seriously, I was getting angry and I didn't really care. I was thinking 'Why on earth is he taking the ball off Palmer?' Palmer's scored five out of five," Shearer told The Rest Is Football podcast.
"He's been the best player for Chelsea, he looks confident when he's taking them. Why would you even contemplate taking it off him? Why would you put yourself forward when you have a record like that?"
Richards said: "It's confidence. Cole Palmer's flying, but sometimes a striker in form would give it to a player who is suffering a little bit in confidence. Just to get his confidence back. No disrespect, it was Leicester at home."
Shearer responded: "What do you mean it's confidence? Bulls***. It's the quarter-finals of the FA Cup, man. Forget about who you're playing or who you want to be nice to and all that s***. Give the penalty to the penalty taker.
"Forget about all that being nice s***, 'I want to get my confidence up' and all that. He's not on the pens. Cole Palmer's on the pens and he's been successful at them, five out of five. Get off, I'm taking it, simple."