The way the pro ranks evaluate rankings is based on the amount of money guaranteed for the tournament, the game. (i.e. 8 ball, 9 ball, 14.1, etc.) It also factors in the head-to-head results, the number of tournaments entered, and how many times the player finished in the money.
A very good table for judging quality of play is a format developed by Pat Fleming of Accu-stats, Inc. It also works really well at the amateur billiard level to judge a player's performance. It is formula based, and you basically feed the algorithm with a billiard league player's various statistics.
The rating formula is as follows:
Number of balls pocketed divided by (number of balls pocketed + number of errors).
Types of errors:
1. pocketing error (you attempt but fail to pocket a ball)2. break error (you scratch or foul on the break or fail to pocket a ball)3. Kick error (if hooked, you attempt but fail to hit the object ball)4. safety error ( opponent can see and pockets a ball after your safety)5. position error (your position forces you to play a safety or miss a difficult shot)
Using this formula, the professional billiard players typically score ratings of .950 to .750. A highly rated pool league player should rate between .600 and .800 against similar competition. At the amateur level, ratings aren't nearly as accurate. In the APA (American pool players assn.) ratings go from s/l 2 (for women) and s/l 3 (for men) up to s/l 7. That's for 8-ball leagues. For APA 9-ball the ratings go as high a s/l 9. BCA leagues (under various league names, such as, VNEA ,or Western Billiards or Colorado Billiards Assn) ratings are based more fairly by ball counts or ball spots, such as weaker player gets the breaks, or, in 9-ball, the weaker player might get the eight or call 7, etc.