I can't really tell what is going on with your angel's fin. The "ball" before the red makes me think it was damaged, maybe bitten...but it almost looks like a red worm attached there, eek!
I'd be tempted to snip off the ball & "worm" but that seems pretty scary & maybe too drastic.
Tell us more about your tank & fish. How long have you had them? What are you water parameters? (ammonia, nitrite & nitrate). Tank size, etc, everything!