Go over twice at speed (5)
I believe the answer is:
oomph
'go' is the definition.
(I've seen this before)
'over twice at speed' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'twice' shows that letters should be duplicated.
'at' says to put letters next to each other.
'speed' becomes 'mph' (miles per hour).
'o' doubled is 'oo'.
'oo'+'mph'='OOMPH'
(Other definitions for oomph that I've seen before include "vital quality" , "Shows excitement aplenty" , "Spirited vigour" , "Vitality, zing" , "attractiveness" .)