Command grabs in Mortal Kombat 11 are special types of throws that are only available to specific characters. These are much stronger than normal throws for two reasons:
1. They cannot be teched
2. They can connect after certain attacks on block
Most command grabs can be used after standing jabs. If the jab is blocked and your opponent continues to block, they will be grabbed. This creates a mixup between doing a jab into command grab and finishing the string. For example, Geras can use Titan Tackle immediately after his standing jab, or complete the entire ,, string. Opponents must guess on whether to jump out of the Titan Tackle or block the ,,.
There is however one problem with using command grabs after attacks. If your opponent is hit by the attack, then the command grab will not connect. This will leave you vulnerable to being punished due to how long the recovery is on command grabs. There is no way to know for certain whether your opponent will block or be hit, so it can be very risky to attempt command grab mixups.
To prevent this from happening, you can option select the command grab to only come out if your attack is blocked. This is done by slightly delaying the input for the command grab. The reason for this is because blockstun lasts longer than hitstun, meaning there is more time to input an attack while your opponent is in blockstun than there is if they were in hitstun. Using Geras as an example again, after inputting his standing jab, slightly delaying the input for Titan Tackle will cause it to only come out on block and not on hit.
While this option select can be quite difficult to do consistently, it gives grappler characters a more complete offense without having to worry about their opponents being hit causing their command grabs to whiff.