Valid/Invalid Fair Catch

[lds7199]

Can a receiver who has given a valid or invalid fair catch signal block during the down? This is one of the questions on Part I of the NFHS test. There has been a lot of debate regarding this question in our organization. I think 9-3-3 says something to the effect of, "A receiver who has given a valid or invalid fair catch signal may not block until the kick has ended." One argument is that the player cannot block during the down because as soon as possession is gained or the ball becomes dead, the play is over. Is there any possible scenario where the person giving a v/invalid fair catch can block during the down? The confusion is based on the word "down". Any help would be greatly appreciated.