Track with bend provides boost for runner? (8)
I believe the answer is:
tailwind
'boost for runner?' is the definition.
'track with bend' is the wordplay.
'track' becomes 'tail' ('tail' can be a synonym of 'track'**).
'with' says to put letters next to each other.
'bend' becomes 'wind'.
'tail'+'wind'='TAILWIND'
'provides' is the link.
(Other definitions for tailwind that I've seen before include "It increases one's (ground)speed" , "Favourable air current" , "Boost for one running" , "Blow to back" .)