Answer: caltrop

AnswerCrossword Clue
CALTROPTire-puncturing strip
CALTROPSpiky device thrown in the road to puncture tires
caltropiron ball with four projecting spikes so disposed that when the ball is on the ground one of them always points upward: used to obstruct the passage of cavalry, armored vehicles, etc.
caltropa spiny plant, also CALTHROP, CALTRAP
caltropany of several plants having spiny heads or fruit, as those of the genera Tribulus and Kallstroemia, or the star thistle, Centaurea calcitrapa