Chap needs a support of course – a ‘cow’ mainly! (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

definition: a manatee may be called a ‘sea cow’, with “mainly” as in ‘the main’=the sea MAN=”Chap” + A TEE [for a golf ball]=”A support of a [golf] course”