One playing matches in legs? (6)
I believe the answer is:
eleven
'legs?' is the definition.
(eleven is 'legs eleven' in the game bingo)
'one playing matches in' is the wordplay.
'one playing' becomes 'v' ('playing' can mean 'versus' in sports).
'matches' becomes 'eleen' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'v' inserted into 'eleen' is 'ELEVEN'.
Can you help me to learn more?
(Other definitions for eleven that I've seen before include "Lowest two-digit prime" , "Number on a side (6)" , "Number, on a team maybe" , "Number of pipers piping" , "Football or cricket team?" .)