Guard Switching is an option select where you guard one direction for a set amount of time, then change directions. This takes advantage of the timing differences between the two attacks and guards against both of them - by blocking in one direction, then switching to the other.
- The opponent performs a crossup
- You recognize this setup and understand that this particular crossup only happens after a set amount of time - if the opponent attempts to hit you before then, then it is not a crossup.
- You block one direction () until the crossup would appear, and then switch to blocking the other direction ().
By changing the direction you block not based on reactions, but on a set timing, you can guard against both situations without worrying about which way the opponent will attack.
This requires that the defender recognize a crossup situation and time their blocking direction changes accordingly. The opponent can play around your expectations by going for different crossups with different timings or ways to block!
This same principle can also be applied to high/low mixups (~).