On top of being small, they may be limited (5)
I believe the answer is:
overs
'they may be limited' is the definition.
The definition suggests an adverb but the answer is not.
'on top of being small' is the wordplay.
'on top of' becomes 'over' (I've seen this in another clue).
'being small' becomes 's' (abbreviation - e.g. clothes size).
'over'+'s'='OVERS'
Can you help me to learn more?
(Other definitions for overs that I've seen before include "Series of balls in cricket" , "Bowling spells" , "Periods of play" , "Sets of six balls bowled" , "Divisions of a cricket match" .)