Injustice 2 players discovered a hack involving PS4's Remote Play option that lets you farm loot boxes without playing the game (via US Gamer). The general idea is to play Injustice 2's Endless Mode by letting the AI control a character and wrack up experience points and loot boxes, which hold a randomized assortment of gear for characters.
Normally you have to press X before each match to instruct the game to begin the next endless match. You watch the AI-controlled superheroes and villains duke it out, a winner is declared, then you have to press X to call up the next match. However, a Reddit user worked out a way to bypass the need to press a button, effectively allowing you to start a tournament and then go do other things while characters beat each other to death and gather experience points and loot boxes on your behalf.
For the hack to work, you need to set up Remote Play communication between your PS4 and PC. Download an AutoHotKey system and program it so that your computer "presses" the Enter key at certain intervals, such as every 30 seconds. Full instructions are available in the Reddit thread, or you can refer to my screen grab of the thread below.
The downside is that if your character loses, you have to manually reset Endless Mode; there's no way to wire up an AutoHotKey instruction (yet). Your best bet is to start a tournament and stay within the vicinity of your PS4 in case you need to get another tournament up and running.