Player’s fast, completely runs into self (7)
I believe the answer is:
allegro
'player's fast' is the definition.
'allegro' can be an answer for 'fast' (I've seen this before). I'm not certain of the 'player's' bit.
'completely runs into self' is the wordplay.
'completely' becomes 'all' (synonyms).
'runs' becomes 'r' (cricket abbreviation).
'into' means one lot of letters goes inside another.
'self' becomes 'ego' (synonyms).
'r' placed into 'ego' is 'egro'.
'all'+'egro'='ALLEGRO'
Can you help me to learn more?
(Other definitions for allegro that I've seen before include "A fast piece of work" , "musical term" , "Old car" , "Scored at a brisk speed" , "'Brisk and lively, musically (7)'" .)