More challenging to catch ball for keeper (7)
I believe the answer is:
hoarder
'for keeper' is the definition.
(someone who hoards or keeps hold of things)
'more challenging to catch ball' is the wordplay.
'more challenging' becomes 'harder' ('hard' can be similar in meaning to 'challenging').
'to catch' means one lot of letters goes inside another.
'ball' becomes 'o' (letter resembling a ball).
'harder' going around 'o' is 'HOARDER'.
(Other definitions for hoarder that I've seen before include "Person acting like a squirrel" , "Accumulator" , "One who accumulates or stockpiles" , "One who accumulates things" , "One saves" .)