Be master of hot early swing (4,4)
I believe the answer is:
hold sway
'be master of' is the definition.
(to hold sway over is to control or be master of)
'hot early swing' is the wordplay.
'hot' becomes 'h' (abbreviation eg on taps).
'early' becomes 'old' (similar in meaning).
'swing' becomes 'sway' (synonyms).
'h'+'old'+'sway'='HOLD SWAY'
(Other definitions for hold sway that I've seen before include "Have the upper hand, rule - sadly who?" , "Have power and influence over - how sadly?" .)