Comment by yxwvut

I'm 99% sure that it originated in climbing - it's been a term since the 80s at least (short for ascend - to 'send' a climbing route is to climb it successfully without falling or weighting the rope). Outside climbing I first noticed its use in the mid/late '00s in mountain biking (which has a fair bit of overlapping user base), and then in other extreme sports. In the jump from climbing to other extreme sports it became a shorthand for 'commit and do something difficult/risky successfully' (similar in spirit to its meaning in climbing if not literally given the etymology).