I have had two of the stranger spares (in my opinion). Several years ago, I (righty) left a 3-8-10. Don't ask me how I left it, but I managed to throw a better shot on the spare (basically my strike ball) and picked it up.

The other one I have left (and picked up) was a 1-5-7-10. It was the last night of bowling one season, and I was messing around throwing a teammate's plastic ball and left it. Figuring that I had no chance to pick it up, I lined up to take my normal shot at the spare. The 1-5 deflected into the 7 and the head pin bounced off the wall and rolled straight across the lane into the 10. If I hadn't done it or seen it, I wouldn't have thought leaving that spare was possible let alone picking it up.

I have also left the same spare dgarren mentioned earlier. The first practice ball on a league night, I pitched the ball out to the gutter and caught some oil. It came back and took the 6-9 out of the rack. When I threw the next ball, I managed to hit the pocket, but nothing was left to deflect into the 10 so it was left standing.

Last year in a sweeper, I left the 2-4-6-8-10.  I probably coulda picked it up if I hadnt been laughing so hard.

I once had a bowler pick up the 7-10...........on his 1st. ball !  I don't remember if he got the other 8 on his spare shot.  I was laughing too hard.

I know this thread was in the Sport Bowling section a while back, but the oddest one I've ever seen is a right-handed bowler at the 2006 US Open who left the 2-5-9.  Not surprisingly, he picked it up.

He missed right, and hit the 3-6 at an angle where the 3-pin was shot between the 2-5 and took out the 4-7-8; the 4-pin then went off the side wall and rolled around and took out the headpin. The ball took the 6- and 10-pins straight back without hitting the 9-pin.

I dubbed it the center rail!