Lag having arrived behind schedule holds us back (8)
I believe the answer is:
insulate
'lag' is the definition.
(thesaurus)
'arrived behind schedule holds us back' is the wordplay.
'arrived' becomes 'in' (I've seen this in other clues).
'behind schedule' becomes 'late' (I've seen this before).
'holds' means one lot of letters goes inside another.
'back' says the letters should be written in reverse.
'us' backwards is 'su'.
'in'+'late'='inlate'
'inlate' going around 'su' is 'INSULATE'.
'having' is the link.
(Other definitions for insulate that I've seen before include "Cocoon" , "Lag" , "Protect (from, eg, heat)" , "Protect from heat, cold, noise etc" , "Thermally protect" .)