i built this with some other guys tonight on Overwatchers server on the sf_silencev2 map
oh yeah, and for people there, this is sharpe|oly
Its somewhat hard to tell from the screenshots, but here is how it works
There is a double crawler leading up to the flag with planks to make it blocked.
surrounding the flag is a trap. I put 3 blocks around the flag, just enough to make the person have to jump into the trap area, or take the crawler back. It worked really well for awhile, until someone unfroze the trap as you can see here.
here are some other screens