While polo matches were high-society staples in mid-century Hollywood—frequently held at places like the Will Rogers Polo Club in Pacific Palisades or the Riviera Country Club—Marilyn Monroe was not part of that circuit.  A few common points of confusion often lead people to associate Monroe with polo or similar sporting events.   She did have some scenes with horses over the years (her choice of footwear makes it obvious that this was not a familiar hobby).   Monroe was famously a regular guest at The Beverly Hills Hotel (living in Bungalow 1 and Bungalow 7 at different points) and frequently spent time in its iconic Polo Lounge, which features classic equestrian polo imagery.

One of her most famous cinematic lines about the sport comes from Some Like It Hot (1959), when her character, Sugar Kane, talks with Tony Curtis (impersonating a Shell Oil heir):

Sugar: “Water polo! Isn’t that terribly dangerous?”

Junior: “I’ll say. Two ponies drowned under me only last week.”