Sega's hedgehog holds variable speed for many players (9)
I believe the answer is:
symphonic
'for many players' is the definition.
I can't judge whether this definition defines the answer.
'sega's hedgehog holds variable speed' is the wordplay.
'sega's hedgehog' becomes 'sonic' (I've seen this in another clue).
'holds' is an insertion indicator.
'variable' becomes 'y' (algebra).
'speed' becomes 'mph' (abbreviation for miles per hour).
'y'+'mph'='ymph'
'sonic' placed around 'ymph' is 'SYMPHONIC'.
Can you help me to learn more?
(Other definitions for symphonic that I've seen before include "Like a major classical music form" , "Like some poems" , "like Beethoven's Fifth" , "in Mahlerian style?" .)