The sport of boxing has certainly seen better days. If you know the name of even one of the several world heavyweight champions floating about the various federations (OK, "heavyweight" and "float" is an ill-suited mixed metaphor), you're a better man or woman than the rest of us. At best, it's now a niche sport, with a decline similar to what horse racing has experienced outside the Triple Crown events.
But it wasn't always thus. For many years, boxing was one of the biggest American sports, surpassed only by major league baseball. It was bigger than pro football, and far bigger than pro basketball (in its embryonic state) or pro hockey.
As one of the most athletic stars in the Hollywood community, it should come as no surprise that Carole Lombard liked boxing. She occasionally attended fight cards at the fabled Olympic Auditorium in downtown Los Angeles (it's still in existence as the Grand Olympic Auditorium, which is appropriate since it's on South Grand Street) and the American Legion Stadium in Hollywood (which closed in 1959 and is now site of a bowling alley).
In her youth as Jane Peters, sometime in 1921, Carole and brother Stuart received boxing lessons from lightweight champ Benny Leonard, a Los Angeles resident. More than 15 years later, she would put that pugilistic experience to use on the screen.
It came during a scene in her only three-strip Technicolor film, the satirical "Nothing Sacred," Hazel Flagg (Lombard), who is putting on a ruse that she's dying of radium poisoning so she can visit New York, is in danger of being exposed as a fraud. In order to keep things going, reporter Wally Cook (Fredric March) tries to raise her ire, and with it her temperature:
Lombard also received some on-the-set training from boxer-turned-actor "Slapsie" Maxie Rosenbloom, a former light-heavyweight champion, who has a small role in the film.
The "fight" scene is arguably the most memorable part of the film, and quickly became a selling point. Witness the poster above, or this one from Spain:

One final anecdote about Lombard and March: Carole had heard that Fredric reportedly liked to put the make on his leading ladies, so one day during filming she invited him to her dressing room. March began making his moves, eventually pawing his way up Carole's dress -- but when he got past her thighs, instead of hitting the jackpot he found...a dildo. The winner: Lombard, by TKO.