Check the dog's foot pads to make sure they're in good condition. Make sure they are not caked with ice before a pull. Make sure the toenails are not left too long or clipped too short. Either condition can prove painful. A split toenail is very painful condition, and a dog should not compete until it is well healed.
Weight pull can be a very fun and exciting sport.
It's especially fun to watch a little dog beat all of the larger dogs. One of the first weight pull dogs I came to know was a Chinese Crested. These are small, skinny, hairless dogs with the topknot on their heads. Not exactly the type of dog you would picture being a weight pull champion.