Beginning to suspect, went and put one's foot down (5)
I believe the answer is:
speed
'put one's foot down' is the definition.
Both the answer and definition are verbs in their base form.
Perhaps they are linked in a way I don't understand?
'beginning to suspect went' is the wordplay.
'beginning to' suggests taking the first letters.
'went' becomes 'peed' (both can mean urinated).
The first letter of 'suspect' is 's'.
's'+'peed'='SPEED'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for speed that I've seen before include "Race" , "Dispatch" , "Rate of travel" , "Rtae of progress" , "Velocity" .)