The main group of cyclists in a race (7)
I believe the answer is:
peloton
'the main group of cyclists in a race' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for peloton that I've seen before include "cyclists in bunch" , "Main group of cyclists in a race" , "Main body of riders in a cycle race" , "Main packed group in a cycle race" , "Racing cyclists" .)