Make shrill sound in the act of crossing street (7)
I believe the answer is:
whistle
'make shrill sound' is the definition.
(a whistle is a shrill sound)
'in the act of crossing street' is the wordplay.
'in the act of' becomes 'while' ('in the act of' can at the same time as).
'crossing' indicates putting letters inside.
'street' becomes 'st'.
'while' enclosing 'st' is 'WHISTLE'.
(Other definitions for whistle that I've seen before include "Referee's item" , "something needing wetting?" , "Call vainly for" , "Musical with Hayley Mills" , "Pucker up and blow" .)