Put one’s foot in it — small gardening tool? (4)
I believe the answer is:
shoe
'put one's foot in it' is the definition.
(shoes are worn on feet)
'small gardening tool?' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'gardening tool?' becomes 'hoe' (hoes are used for gardening).
's'+'hoe'='SHOE'
(Other definitions for shoe that I've seen before include "Perhaps casual" , "Hose (anag)" , "pump, say" , "What one needs for a horse" , "9 maybe" .)