A game involving two students, versatile players (3-8)

'versatile players' is the definition.
(I've seen this before)

'a game involving two students' is the wordplay.
'two students' can mean two substitutions for 'student'.
'game' becomes 'rounders' (rounders is a kind of game).
'involving' indicates putting letters inside.
'student' becomes 'l' (as in L-plates for learner drivers).
'student' becomes 'l' (as in L-plates for learner drivers).
'a'+'rounders'='arounders'
'l'+'l'='ll'
'arounders' going around 'll' is 'ALL-ROUNDERS'.