Name for this percussion instrument?

Solution 1:

From your description I had to think - same as StoneyB commented** - of an

Ratchet

They are often used at sports events.

** and in the minute of this post also Hugh did

Solution 2:

'Ratchet' is clearly the American word, and is the Wikipedia entry. (+1 @Daniel)

So, purely for completeness:
'Football Rattle' is usual in Br English, even though many Clubs have banned its use. There are also two manufacturers making them for percussion instruments, qua ratchets, clackers, rattles and even football rattles.

http://www.knotjustjigs.co.uk/football-rattle-football-clacker-286-p.asp

http://www.americanbell.org/forum/viewtopic.php?f=11&t=4341

http://www.dailymail.co.uk/sport/football/article-2464574/New-Anfield-exhibit-seen-treasures-Liverpools-history.html

http://www.jampercussion.com/buy/percussion-plus-football-rattle_687.htm