Mortal Kombat 1 has been officially announced as releasing in September of this year, but a lot of fans are wondering if the game will have a rollback netcode, while other fans are wondering what the hell rollback netcode actually is.
Rollback netcode is a type of online communication used for fighting games that is supposed to reduce latency as much as possible, so that everything feels more responsive and so that competitive players don't have to deal with losing a game due to circumstances beyond their control.
Mortal Kombat 1 will have rollback netcode. According to the official FAQ, 'Mortal Kombat 1 will have rollback netcode to support online gameplay.'
Earlier in the same FAQ, they also commit to the fact that an online connection isn't necessary to play the game, meaning that you can play the game however you want. With the game launching only on next-generation systems (and Switch, but likely through a cloud host), it's important to make sure that the game is as polished as possible.