sandbag (sand|bag)

noun

• a bag filled with sand, typically used for defensive purposes or as ballast in a boat.

verb (sandbags, sandbagging, sandbagged)

• 1 (usually as adjective sandbagged) barricade using sandbags: boarded-up shopfronts and sandbagged doorways

• 2hit or knock over with or as if with a blow from a sandbag.
• North American coerce or bully: he was trying to sandbag me into attempting one of his leg-snapping climbs

• 3 [no object] deliberately underperform in a race or competition to gain an unfair advantage.