I seem to have a strained pectoral muscle.
It might have gotten hurt Friday dueing kickboxing when I blocked a high kick with my arm. It's been a little sore, but tonight when I was grappling, when people put pressure on my chest it was intensely painful. Then in sparring it was mildly sore and not an issue.
I've never heard of a strained pec, but I suppose any muscle can get pulled.