My understanding from a long time in theatre is that yes, it is bad luck to wish an actor "good luck". So as not to jinx the show, it is proper to say break a leg because that is the worse thing that can happen in a performance. Thus by wishing it, it never happens.

Whistling, at least in the Circus, is considered bad luck and is forbidden. Music, including music from radios, etc., was also forbidden in the clown alleys of the older shows. I believe that the bigger shows still observe this rule such as Royal Hanneford and RBBBC.

It is also forbidden for Circus clowns to wear green face paint. If a clown is wearing green face paint, she or he is not a trained, apprenticed Circus clown but rather one of those people who paint their faces and make balloon doggies.

When a performer enters the ring. she/he must enter right foot first; to do otherwise is bad luck for the show. (Off topic circus trivia: The person who announces the acts is traditionally known as the Equestrian Director. Ringmasters were originally the human performers on a pony or horse act.)

In Baseball, you will see MANY managers, coaches, and even some players purposely step over the foul lines when walking or running onto the field.

One last bit about Baseball: The home plate umpire ALWAYS brushes off home plate with his back to the pitcher. This has nothing to do with luck and everything to do with the infamous 1894 Baltimore Orioles managed by Ned Hanlon and captained by the legendary John McGraw. The 1890s game of Baseball was very vicious. In fact, historian Bill James called it downright criminal. Spikings (remember, these were sharpened steel spikes in those days, not the cleats players wear now), fractures, bean balls, brawls, etc. were the norm along with other more creative nastiness. One of them was the practise of kicking the Umpire on his rump when he bent over with his back to the catcher!

It IS interesting to note that actor John Wilkes Booth suffered a broken leg after he assasinated President Lincoln. As he jumped from the President's box at Ford's Theatre he shouted "sic semper tyrannis". Apparently, a spur on one of his boots caught the bunting on the way down and he broke his leg.

Best,
Vlad