Call of Duty: Modern Warfare
In the campaign level Captive, Farah Karim uses a rock during her escape from her prison cell. She throws it at a button that opens all of the cell doors, allowing her access to the rest of the prison. If she runs out of rocks, she can use the makeshift shiv to carve out more rocks from a nearby hole with relatively weaker rocks.
Rocks are also a weapon which players use in certain Trials.
Call of Duty: Warzone
When an eliminated player is sent to the Gulag, they are able to use rocks while waiting to partake in a fight, throwing them at participants and dealing 1 point of damage. If a kill is earned with a rock, the attacker will not be redeployed.