What is the difference between offensive and defensive chairs?

Wheelchair Rugby Canada's equipment guidance groups chairs by the class of the player:

• Offensive chairs are for classes 2.0, 2.5, 3.0 and 3.5, with a low-profile front bumper and wings.
• Defensive chairs are for classes 0.5, 1.0 and 1.5, with an extended front bumper to hook other players.

Spoke guards are mandatory. The equipment manager is allowed one minute on court for equipment repairs. All players compete in manual wheelchairs.

Sources: https://wheelchairrugby.ca/equipment-management/ and https://wheelchairrugby.ca/the-sport/