Item 3: Muff
After a valid fair-catch signal, the opportunity to catch a kick does not end if the ball is muffed. The player who signaled for a fair catch must have a reasonable opportunity to catch the muffed ball before it hits the ground without interference by members of the kicking team, and regardless of whether the ball strikes another player or an official.
Rule 10, section 2, item 3. There was a change made in 2010 after the Titans caught a ball that bounced off the returners chest in stride and ran into the end zone, and were penalized 15 yards for fair catch interference. Now the yards are waved off in that case, but the ball remains with the return team.
Of course, there's no explanation for what a "reasonable opportunity" is considered to be.
This post was edited on 11/25 at 9:59 pm