from Jude Rosenstock:
D - Will appear as though they are stumbling through the rack. Their occasional run-outs will either consist of very easy layouts (which they will nearly mess-up), a few lucky shots and/or unintentional position.
C - Greater sense of cue control and much more of a deliberate appearance than a D. They will undoubtedly run out with BIH with 3 or 4 left and will make it look routine but are suspect beyond that.
B - Really the beginning of the run out player. If they make a ball on the break and get position on the 1 ball, they should have a reasonable expectation to get out. Any cluster or unusual position play will diminish their chances significantly. Usually, B players possess unusual strength in either pocketing, strategy or position play. Rarely two of three, never all three. Their creativity is usually limited at this level but you may begin to see glimpses of what's to come.
A - Definitely catagorized as a run out player. They are supposed to capitalize on most mistakes. Greater attention is paid to more subtle details. Expect a consistent and strong break and strength in multiple attributes (pocketing, defense, position play, creativity). Most noticeable among players at this level and above is an aura of confidence.
Open & Above is very similar to what you see described in A only more refined. You will see advanced to expert break, pocketing, defense, position play and creativity. Low level opens might be advanced in all of these catagories while world class professionals might be experts in most or all. All of these players are expected to run out with any routine opportunity. Any run-stopper situation (clusters, blocked position routes) is expected to be handled in such a way to still give the shooter an expectation of winning.