How do I rule when the ball hits a player, or the striker holds up for fear of hitting the opponent?

Ball hits the non-striker on its way to the front wall (Rule 9.1), stop play:

• Return wouldn't have been good: non-striker wins the rally.
• Going directly to the front wall, first attempt, striker hadn't turned: stroke to the striker.
• Had hit or would have hit another wall first, striker hadn't turned: let, or stroke to the striker if it would have been a winning return.
• Striker hadn't turned but was making a further attempt: let.
• Striker had turned: stroke to the non-striker, unless the non-striker deliberately moved to intercept the ball (then stroke to the striker).

Ball hits a player on its way back from the front wall (Rule 9.2):

• Hits the non-striker before the striker has attempted a shot, no interference: striker wins the rally, unless the striker's position caused it (let).
• Hits the non-striker after one or more attempts: let if the striker could have made a good return, otherwise the non-striker wins the rally.
• Hits the striker with no interference: non-striker wins the rally.

Striker holds up rather than hit the opponent (front-wall interference, Rule 8.11):

• Ball would have hit the non-striker on a direct path to the front wall: stroke, unless the striker had turned or was making a further attempt (then let).
• Would have hit the non-striker then a side wall, or a side wall then the non-striker: let, or stroke if it would have been a winning return.
• Wouldn't have hit the non-striker: apply the general interference rules.

If a striker hits the opponent with the ball, always consider whether it was deliberate or dangerous.