That looks rather like a 'Peruque' or 'Wig' head which is a rare freak antler growth which sometimes occur in male deer- usually Roe, if their antlers or testes are damaged, though in that case they normally remain covered in velvet (hence the 'wig' name). But it also looks like this deer's antlers might have been sawn which could have caused this.
Although its in a Milu park, it seems this is a Sika(?)
Not certain, but I think that could be a castrate. Late castrated deer continue to grow velvet antlers which dont harden properly. Never seen one like that before though.
Being a fallow with people standing behind it I suspect it is a castrated pet.
I think it may be a Sika though other photos show both are present here...
As visitors seem able to enter the enclosures, maybe they have dehorned some of/all the males to make them safe, perhaps some are castrated too which has caused this abnormal growth.
