Run over sickly tree (5)
I believe the answer is:
rowan
'tree' is the definition.
(type of tree)
'run over sickly' is the wordplay.
'run' becomes 'r' (cricket abbreviation).
'over' becomes 'o' (cricket abbreviation).
'sickly' becomes 'wan' (I've seen this before).
'r'+'o'+'wan'='ROWAN'
(Other definitions for rowan that I've seen before include "Tree bearing bright red berries" , "Mr Atkinson, actor" , "Atkinson or Williams" , "ash native to mountain regions" , "Tree with orange-red berry-like fruits" .)