In light of the recent post regarding two sibling SBT fighting I thought I would go back thru my picks and there are plenty of pictures showing when the puppies started to play fight.
Going from pictures it started at about 3 weeks of age.
couldn't resist this fat full tummy
and a preggers whippet mum about a week out from whelping.
Whippets are generally quiet dogs, not barkers but when they play fight the sound is frightening.