I'm dying laughing at all these answers I've read so far. Here's the correct answer if anyone's interested.
A: Cue ball is rolling forward, like a gear turning in rotation.
B: Object ball is stationary, meaning not turning at all.
C: Friction is what takes place when the cue ball first comes into contact with the object ball.
D: What happens is that you have one moving object trying to move a stationary object.
E: Resistance is when the cue ball makes contact with the object ball, and before the object ball can move from it's stationary position the cue ball surface....spining/rolling like a gear at a downward angle at the point of contact on the object ball encounters friction/grip/grab/hold on...or what ever you want to call it...and actually tries to climb up onto the object ball for a split second before that friction is broken, and in doing so that friction is enough to cause the cue ball to hang onto the object ball and alter the course of the intended shot.
Some of the answers given are semi correct, Russ was right in saying that if you add a little side spin to the cue ball it'll break that friction grab...well, that's right because now the cue ball is not spinning in a straight forward spin which is what it has to be doing in order to compound that friction collision, so alter the straight forward spin is one answer.
Fatboy is kind of right as well, but not for what he thinks. Simonis has not changed it's 860 10% nylon 90% weave in the last 20 years or so. But when it first came out it was an upgrade to 760 Simonies being 30%nylon 70% wool it just had thicker threads so to speak, making it a thicker 177 threads per square inch cloth over the 177 threads per square inch 760.
But, the second part of friction is the spot in the cloth the object ball is sitting. In order to create that environment for the cue ball to jump up on the object ball...the object ball is to be able to sit where it's at for that split second, and that's what dirty cloth can do...add friction to the ball to help cause it to want to sit where it's at and not want to move...until force moves the ball.
Dirty surface of the balls adds friction, and believe it or not, over waxing or the wrong wax can cause that same cling/friction to happen.
Speed plays a major role in that friction cling as well, because a cue ball traveling to fast...or to slow is not going to create that perfect cling on the object ball.
Angle of cut has a lot to do with friction as well, because the cling/grab/jump of the cue ball only can happen when it's a glancing contact. Full contact is impacted more by the full weight of the cue ball and therefore harder for the cling to take hold on the object ball enough to lift the cue ball off the surface of the bed cloth.
So, one of the most key ingredients to get that little cling/jump/grab to happen....is the straight roll of the cue ball, at the perfect angle of cut...and you have missed your shot.
Avoid that from happening by simply altering the natural roll of the cue ball by playing any English on the cue ball that will offset it's natural roll/spin and you can't have cling.
NO cling can happen with draw or side spin on the cue ball, provided the cue ball is still spinning in a back-wards/off center rotation at the moment it comes into contact with the object ball.
Top/follow English WILL enhance the cling provided the angle and speed of the cue ball is a match to enhance the cling.
Glen