whats the difference?
Bump = Short roll. When you're bumping a dog you're not evaluating the dog, you'd do it to get one started or let one get the feel of actual contact.
Roll = well, a roll This is where the fun begins, because it's here you're evaluating your dog, schooling him, seeing if he's got what it takes to be a show dog, or not . It's here where he will show you what style he is, or how game he is if you want to check it. A roll is essentially a sparring session, there is no set time limit and you're free to pick your dog up whenever you want.
If I were to bump a dog it would be to know were he stands maturity wise. You don't even need contact to be honest. Just face him and you'll most often know. If not A quick bump will let you.
Of course you need contact, it's all about the contact.
Allowing your dogs a back yard barkoff is telling you nothing about those dogs, other than they'll show aggression when faced with other dogs; although usually a good indication, it's not a clear indication that he's on, actually going over and taking hold is, and that's why you need contact because you'd be a fool to judge a dog on how it acts.
I agree contact is needed ive had a few dogs who showed no care for other dogs until they were in the box, you could walk a pissed off dog up to them on the chain and they could care less and when they were across from the same dog in the box it was a totally diff story.
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Actually, this is where a lot of people blow it.
A roll is supposed to be to school the dog, not necessarily to judge him yet.
Your first few rolls should be against dogs of different styles, to teach your dog how to handle them, and these rolls should be fairly short (< 15 min). You really shouldn't be passing judgment here, but instead assuming the role of educator.
Only after you first invest the time allowing your dog to mature, and educating your dog in the process by exposing him to dogs of various styles, should you then place him in a serious hard roll (or match) to evaluate him for real. Too many people want to game test their dogs damned near the same day they first start, which is a mistake.
Naturally, during the schooling process, if the dog is an ace (or a bum) you can see these levels of ability as you go along ... but his gameness shouldn't be seriously challenged at all ... until he is FULLY-mature, FULLY-started, and FULLY-schooled
Jack