Blocking is a form of bow-crossing meant to physically impede the passage of another ship to its destination. Blocking is typically used by Chinese ships to hinder other countries from resupplying or reinforcing their outposts in the South China Sea.

Distinct from other forms of bow-crossing, blocking is used for area denial rather than operations disruption and will often result in more protracted stand-offs. China uses this tactic to assert its claims of jurisdiction as well as to prevent certain activities--most notably the reinforcement of other claimants' existing Spratly Island outposts.

One such blocking maneuver occurred on April 26th, 2023, when China Coast Guard (CCG) ship 5201 blocked the path of the Philippine Coast Guard (PCG) patrol vessel BRP Malapascua. This forced the much smaller PCG ship to abort its planned route to the entrance of Second Thomas (Ayungin) Shoal during a resupply mission to the Philippines' outpost aboard BRP Sierra Madre: 

China routinely prevents the entry of Philippine ships into the interior of Second Thomas Shoal as a cornerstone of its strategy to prevent the rusting outpost from being repaired or replaced until it breaks up or otherwise becomes uninhabitable. For nearly a decade it has allowed only small wooden boats carrying food and replacement troops to pass through its blockade.

Other examples: 

On September 19, 2019, also near Second Thomas Shoal, a CCG ship blocked Philippine civilian vessels while they were conducting a resupply mission to the BRP Sierra Madre.

On November 13, 2015, about 13 nautical miles from Subi Reef, CCG cutters 35115 and 2305 blocked the path of a Vietnamese replenishment ship heading towards the Vietnamese outpost on Southwest Cay, forcing the ship to find a different route to its destination. PLA Navy Type 072A landing ship 995 later blocked the ship's path again, this time brandishing small arms and firing a warning shot.

See the rest of the playbook here.