What safety device is activated when the lever action is pulled tight against the stock of a firearm?

The trigger block or lever safety is designed to prevent the firearm from discharging unless the trigger is intentionally pulled. When the lever action is pulled tight against the stock, this safety device engages to block the trigger mechanism from functioning. This adds an important layer of safety by ensuring that even if the weapon is accidentally dropped or mishandled, it will not fire if the trigger is not pulled deliberately.

Other types of safeties serve different functions: the hammer safety typically prevents the hammer from falling unless the trigger is pulled; the magazine safety prevents the firearm from firing unless a magazine is inserted; and the firing pin safety blocks the firing pin from moving forward unless the trigger is pulled. Each safety has its specific role, but in this context, the trigger block or lever safety directly relates to the action described, making it the correct answer.