Number 11, whoa.

Reddit comment:

For the layman, there's one big reason why these professionals don't just bowl a perfect game every time, which (like darts or billiards) seems like it would be much more common than only 24 times in the history of televised bowling. That reason is the oil patterns on the lanes for the professional circuit compared to what the average Joe bowls with. Average Joe gets a lane with a much more predictable and reliable oil pattern that develops due to the rather random nature of amateur bowlers. The professionals essentially bowl their first ball in exactly the same pattern over and over again, and the oil becomes thinner and thinner in this channel. Even slight deviations from the channel results in rather unpredictable behavior. The oil is also deposited onto the surface differently for professional tournaments compared to your local alley, and this has a big impact on difficulty. This is why perfect games on TV are rather rare, even though high school kids are capable of doing it at their local alley.

Edit: read this and/or this and/or this for more info on oil patterns. Also added oil patterning and some grammar corrections.

500 Reddit comments:

http://reddit.com/r/videos/comments/2qrus8/guy_bowls_300_in_pba_semifinal_only_the_24th/