the ball slide down the lane, will either hook , backup or go straight depends on the thumb and finger exit sequence. and the drilling whether is it conventional grip or finger tip grip. there are very detail analysis and discussion on chinese forum.
1. not every one turn their wrist before approach, some turn to get high rev rate. Just like Ring finger lead concept.
2. Spare ball is good for very dry condition, in china and taiwan most lane are not oil regularly maybe once a day due to economical reason. that why they hardly can play hook. Some change to spare ball when hitting the back row of pin to prevent the ball from hooking or back up too much. just like the concept of Hook player change to spare ball when hitting pin 10 or pin 7 on different lane condition. Some prefer hard surface for pin action some prefer softer surface to grip the lane . I myself use 800 grid sand particle on medium oil lane. on dry lane my ball basically lost all the energy it needs.
3. They change ball, i think is the ball pin reaction is not ideal. if the ball is too dull, alot of energy is lost when the ball hit the pin. If the ball is too shiny, the ball skid in and didnt grip the lane to increase speed from the rev of the ball. Just like the concept of hook ball. if the ball dont go into roll and skid into the pocket, the hit is very weak. If the ball roll out and lost energy, the hit will be weak. too.
4. the rotation is to have maximum axis tilt. upon release the thumb is face down. To hook player it is regards as too much axis tilt. the oil track is very low, so it dont hook much and the contact is lesser and friction is lesser too, therefore a lot of engergy is store and unslash when hit the pin. the ball weight is only 11-12 pound, it getting the pin action of hook ball 14-16# pin action. Lighter weight helps to rev easier. to light, the carry suffer, therefore mostly use between 11.0-12.0. However this style suffer if playing on heavy pin like PBA gold pin, i heard from top helicopter player.
14# No Mercy Beatn(heavy oil ball)
14# Black Widow medium oil
14# Lane 1 hrg
15# red alert edge
12# columbia spare ball
Oil Trek(axis tilt): high.
40 games across 6 centers league avg :170