My dad was in deep rough...taking practice swings and looking at his target...getting a feel for the shot/rough. To his surprise when he was looking up and taking practice cuts a ball flew out...which was not his...and he was unaware of.

Any penalty?

Thanks guys.

Good Q.

I am curious as well.

My guess is no.

Also, it really wouldn't matter unless it was in tournament play.

No penalty.
Good old decision 7-2/7. Since the player clearly had no intention of striking the concealed ball, his/her swing remained a practice swing and was not a stroke. Consequently, there is no question of his/her having played either a practice stroke (rule 7-2) or a stroke with a wrong ball (rule 15).

No penalty. He did not make a stroke at the hidden ball.

Thank you.

On a similar note....I once hit my own ball out of the deep rough and TWO balls flew out (mine and an embedded ball underneath). What would be the ruling on this?

Same. You played yours properly and count that shot, but you can forget about the other one. Intent to hit one but not the other.

Could this rule be applied to hitting your ball on a practice swing? Although it sounds like a dumb question I've had moments where on the first tee, I stupidly made a practice swing over the ball while looking at the target not the ball and mitakenly topped it. I took a first hole mulligan......lol

On the tee, the ball is not in play until you hit it with an intentional stroke, so in that case you can have a laugh over the top, then put it back and play your first shot.

If you have already teed off and it happens in a subsequent shot, you have accidentally moved the ball and must take a penalty and replace it.