Team in taxi missing reserves (6)
I believe the answer is:
eleven
This clue could be a double definition.
'team in taxi' is the first definition.
'eleven' can be an answer for 'team' (eleven is a kind of team). I'm not sure about the 'in taxi' bit.
'missing reserves' is the second definition.
'eleven' can be an answer for 'reserves' (thesaurus). I'm not sure about the 'missing' bit.
(Other definitions for eleven that I've seen before include "football team, for example" , "'Legs' bingo number" , "Cricketing side" , "Players" , "Time for morning coffee" .)