What are the chances? Two players, both playing from just off the green hit their balls at roughly the same time, and while both balls are in motion, the balls collide. It happened at Oceanside Muni.
I've just read Rule #11 three times, and I'm clear on the ruling in this scenario. No penalty to either player, both players play their ball as it lies. I can imagine a lot of other scenarios that are less clear. We'll start with the ones that are clear.
The violation we regularly encounter of Rule #11 is when you're putting, and your ball hits another ball at rest on the green. This is a two stroke penalty on the person who putted. A lot of people think the penalty should be on the person who didn't mark their ball. It's not. You need to ask the other player to mark his ball. This is a loss of the hole in match play.
Another situation frequently encountered is a ball played from off the green hits a ball on the green. There is no penalty in this situation, and the ball that was played must be played as it lies (Rule #11). The ball that was struck must be replaced as close as possible to the previous position (Rule #9.6). Actually this applies in any scenario except when both balls were on the green.
So what would happen if we were both putting? My interpretation is that there would be no penalty, based on the phrasing of the exception to Rule #11.1a, which states in part "If a player's ball in motion hits another ball at rest..." So this would be the same as if the ball hit another players equipment (unintentionally).
Does it matter which player was away? Not as far as I can tell. There is no penalty for playing out of turn in stroke play.
But this could also get weird in match play. If both players play at the same time, and the collision occurs, then the player who was away could decide to cancel both strokes if he doesn't like the result. There is no penalty for playing out of play in stroke play, but in match play, the person who did not play out of turn can cancel the stroke.
Another common related misconception is that a player is away if their ball is off the green, and another player is on the green. Play order is determined strictly by distance. It doesn't matter what surface the ball is in / on. So if a player is in a bunker, and another player is further from the hole, but on the green, then the player on the green should putt. I will often violate this rule for pace of play. Let the guy in the bunker play first, and then he can rake while I putt.
Related - If your ball is at the bottom of a lake, but closer to the hole than your opponent, then your opponent is away until you drop.
