Coming up, strike boss (4)
I believe the answer is:
knot
'boss' is the definition.
(both can mean a lump or mass of material)
'coming up strike' is the wordplay.
'coming up' says the letters should be written backwards.
'strike' becomes 'tonk' (informal term meaning to hit).
'tonk' reversed gives 'KNOT'.
(Other definitions for knot that I've seen before include "Shore bird, tangle" , "Something tied" , "Could be a granny or a sheepshank" , "securing tie" , "A sheepshank or bowline" .)