This skydiver deployed their main canopy and had a bag lock, so they cutaway and deployed their reserve. However, the cutaway didn't fully release and their un-deployed main began trailing behind them. They managed to disconnect it by pulling on the riser, reeled it in (lines flailing and all), held it between their legs and landed with it. Note: this is NOT advisable.
Several factors can contribute to a bag lock: long line stows can lock each other off, a stow can get pulled into a grommet, a pilot chute can be in need of replacement, etc. We would need more information to make a definitive statement about what specifically caused this bag lock.
It’s hard to see what this jumper’s hands were doing once they decided to cutaway. The first thing that comes to mind is that they didn’t pull their handle all the way or that the cables were too long, but it appears like they dropped the handle so that may not be the case. One alternative is that there could have been a mechanical issue like the shackle from their RSL could have jammed their three-ring.
We make this statement more than any other: take packing seriously... Every. Single Time. Don’t rush, go step-by-step and don’t let yourself get distracted or complacent. When it comes to preventing bag locks, a few steps are particularly important: make sure to cock your pilot chute and don’t put too much (no more than 2 inches) excess through your stows; it can help prevent the stows from potentially catching each other.
Skydiving gear is not cheap so the instinct to reel in a main during an incident like this is understandable. However, it’s not the safest option for a few reasons. First, it distracts you from focusing on a safe landing and – especially if you’re landing off already – that needs to be your top priority. Next, all those lines flying around could have easily wrapped around this jumper’s hands, risers, etc., and escalated this situation into something even scarier. Last, as one individual who viewed this video noted, the main was creepy close to coming out of the bag as this jumper reeled it in. Had it deployed it could also have potentially made this situation worse.
Fortunately, this jumper was able to fully release this incomplete cutaway with nothing but a tug on the riser. Had that not worked and the main actually deployed, they may have been in a position where they would want to cut that riser. We don’t know if they had a hook knife, but this could have easily become a situation which warranted one. (So, as we’ve asked before, is your hook knife part of your gear checks?)