One fighting hard, someone at crease collecting half-century (7)
I believe the answer is:
battler
'one fighting hard' is the definition.
(someone fighting a battle)
'someone at crease collecting half-century' is the wordplay.
'someone at crease' becomes 'batter' (batters stand at the crease in cricket).
'collecting' indicates putting letters inside.
'half century' becomes 'L' (Roman numeral for 50).
'batter' placed around 'l' is 'BATTLER'.
(Other definitions for battler that I've seen before include "Fighter" , "One struggling" .)