In Super Smash Bros. for Wii U, getting grabbed at high damage percentages usually means certain death, due to a large portion of the cast having a kill throw. For other characters, they need to rely on DI traps to secure that killing blow. In their quest to teach players more about Smash 4, the Beefy Smash Doods have dedicated a video to the ins and outs of DI trapping your opponent.
For those who don’t know, a DI trap is where you put an opponent in a situation where DI-ing a certain way may lead to a combo or to their death. In most cases, players will use a DI trap when their opponent is expecting them to use a certain follow-up, and pre-emptively DI in order to avoid it. If you catch onto their pre-emptive DI, you can set up a kill which wouldn’t normally work.
Some throws are so slow that you can actually react to their animation and avoid the trap, while others require you to option select your DI. With a DI OS, you simply input one direction before the throw begins, then quickly switch once the animation begins. This can be beaten by your opponent simply waiting before they start the throw, but you could always mash out in that small window.
Source: Beefy Smash Doods