Heads of such knockabout institutions go downhill fast (3)

I believe the answer is:

ski

'go downhill fast' is the definition.
(I've seen this before)

'heads of such knockabout institutions' is the wordplay.
'heads of' indicates taking the first letters.
The first letters of 'such knockabout institutions' is 'SKI'.

(Other definitions for ski that I've seen before include "Slide downhill, sportingly" , "Winter sport item" , "Sport on piste" , "Winter sport equipment" , "Mountain runner" .)

I've seen this clue in The Times.

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