Regarding bowling actions.
The law about the bowling action comprises three parts:
The stride, the action and the release. We all know about the stride (e.g. overstepping, etc). The action and release laws are quite misunderstood, so I will try and put it as clearly as possible here.
The following conditions apply:
1. If a bowler enters his action at the top of his arc with his arm bent at the elbow with an angle greater than 15 degrees, he may not straighten his arm during release.
2. If a bowler enters his action at the top of his arc with his arm straightened, he may not bend his arm more than 15 degress during or immediately before release.
3. A maximum of one revolution of the arm throughout the delivery action is permitted.
4. A bowler may flex and rotate his wrists as long as the above are adhered to.
5. A bowler may not leverage the angle created by hyperextending his elbow (extend his elbow joint by a negative angle with respect to the upper arm)
There is no restriction on the trajectory, though there are other restrictions such as the ball may not bounce more than twice and rolling deliveries are not permitted.