Cooperate (6)
'co-operate' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for play ball that I've seen before include "meet a delivery?" , "go along" , "Be cooperative" , "Most boys love to" , "Do what is needed" .)
'cooperate' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for liaise that I've seen before include "Work together" , "Act as contact" , "Act as go-between" , "Communicate with for mutual benefit" , "Conduct information between two groups" .)