Skidding occurs when the cue ball, with some follow or natural roll, contacts the object ball at just the right angle, with just the right friction, so as to induce the opposite effect on the object ball that we are all familiar with as they touch. That being reverse or draw. Follow on the cue ball puts draw (or reverse roll) on the object ball.
In other words, the cue ball's forward roll, induces a touch of backspin on the Object ball as they touch. As the two balls contact the follow roll on the cue ball and the reversing effect on the object ball keeps them both in contact with each other for a split second longer than would normally be.
As they seem to cling together they roll off their normal cut angle as a pair of kissing balls. This throws them off line in terms of the normal cut.
The inside english adds to this effect because it prevents the cue ball from rolling off the object ball as it passes.
You'll never see cling, or skid if you hit a center ball or a draw stroke or shoot the shot with a touch of outside english. You need to create that gear effect where the object ball gets a touch of backspin from the cue balls forward roll to make them stay together.
Sometimes the effect is so noticeable that the cue ball seems to want to climb up on the object ball, thats because the object ball wants to backup into the cue ball.
When this effect happens on the newer napless cloth, with less resistance, the effect is able to become more noticeable.
REP to you. IMO, dirty ball are not required. Our pool hall cleans and polishes daily. These balls skid more often. I believe that the polish causes tha chalk to adhere to the cueball. Slow, short, straight shots with follow seem to have the greatest chance to cling and skid. I've actually wiped the chalk off of my tip when this type of shot comes up.
Paul.........try a search and you'll lots of info