Canon EOS-1DX MARK II Settings Manual page 31

Therefore, Case 6 is an effective setting for subjects that
stop and start suddenly, and also have erratic movement
which could change a subject's location in the frame,
and it is recommended when using Auto selection AF,
Large Zone AF, Zone AF, and AF point expansion.
This scene is rhythmic gymnastics with large jumping
movements from a resting position. This setting is
effective in scenes where there are large movements
followed by complete stops in movement.
*With Single-point AF and Spot AF, AF point auto switching
is unavailable, and Case 6 only impacts the AF response to changes
in subject speed.
A rhythmic gymnast making sudden big jumps can be
captured when shooting with Case 6.
31