Bowling reached the height of its popularity as an American recreational pastime in the 1970s, which makes it perfect for inclusion in The Big Lebowski. You may have noticed a pattern developing here: despite living in the early '90s, The Dude has surrounded himself with all things '60s and '70s, probably to remind himself of his heyday as a Haight-Ashbury hippie. It's also a relatively cheap way to spend time with friends and relax.

But bowling is more than just retro scene-setting in The Big Lebowski. It's the central activity of The Dude's life (even though we never see him actually bowl in the film), and bowling ball imagery finds its way into all of his dreams and fantasies. He even blisses out to audiotapes of bowling tournaments. Seriously. Bowling is also a metaphor for one of the movie's biggest themes: fate, and how to control it. The Big Lebowski would have us believe that humans are as easily knocked down as bowling pins, and there's no way to know who or what is doing the knocking.

During the opening credits, when everything seems to be going well, everyone is bowling strikes. But as things get more complicated and tensions rise, people start missing pins. When Walter pulls a gun on Smokey, he's only bowled an 8. Right before Donny dies, he bowls a 9.

Both of The Dude's dream sequences involve bowling. In the first one, The Dude is trapped in a bowling ball. In the second one, he's literally become the bowling ball—flying down the lane through the legs of "pin-headed" women. Although the bowling ball may seem more powerful than the pins it is knocking down, there's still the feeling that The Dude is not in control, that he's just hurtling down the lane ready to crash. (To get the bowling ball point-of-view shots, the Coens attached a camera to a mechanism that resembled a barbecue spit and rolled it down the lane.) (Source)

If you look closely at the photo of the Big Lebowski and his Urban Achievers, you'll notice that the kids are arranged like bowling pins, with the self-important Big Lebowski as the #1 pin in front of the others. In bowling, as in life, some pins that seem more prominent than others will be the first to be knocked down.

Finally, bowling balls are, well, balls. And they have a lot of erotic moments in the film. Remember The Jesus licking his ball? And the two balls flanking the bowling pin in The Dude's pornographic Gutterballs dream? These bowling balls are versatile actors in the film, carrying all different kinds of symbolic weight.