The class workout programmed is a great example of utilizing isometrics within a CrossFit workout.
An isometric is when you hold a static position and try maintaining that specific posture with tension in the muscles you are targeting.
I find it easiest to implement isometrics in a partner workout setting because they can be held while the other partner is performing the work portion or the workout. When choosing the isometrics I like to pick one that will cause interference with the movement it is being performed with because it will keep the athletes work intervals shorter. The shorter work intervals are good because I like to use partner workouts during the week to provide a small deload from volume, due to the nature of volume being so high in CrossFit training. Also you can goose isometric movements to be paired with CrossFit movements that will help the athlete connect with what body part they should be feeling while performing the dynamic movement. For example you could pair a glute bridge with a squat