Evidence of impact speed in outskirts of Chester (6)
I believe the answer is:
crater
'evidence of impact' is the definition.
(impact caused by a meteor)
'speed in outskirts of chester' is the wordplay.
'speed' becomes 'rate' (the speed at which something happens).
'in' means one lot of letters goes inside another.
'outskirts of' suggests removing the centre (only letters on the outskirts).
'chester' with its middle removed is 'cr'.
'rate' inserted inside 'cr' is 'CRATER'.
(Other definitions for crater that I've seen before include "Bowl-shaped hole in the ground" , "Caldera" , "Large hole" , "Volcano opening" , "Bowl-shaped depression" .)