Here is the ABBI's description of how to judge "buck."
"The term 'buck' refers to the height achieved with the front feet and shoulders as a bull begins each jump of a trip. Technically correct bulls will complete this action by kicking their hind legs, however not all will kick, and that is a separate category from buck. Bulls that “get in the air” and get their front feet a foot or two off the ground as they peak and break over get the most credit in the buck category. Another consideration is the number of jumps they complete during the course of the trip. Still another factor can be how much ground they cover."
