Sabotage isn't very nice: It's when you ruin or disrupt something by messing up a part of it on purpose. Loosening the blades on your competitor's ice skates would definitely be considered sabotage.
Sabotage comes from the French word saboter, which literally means “walk noisily.” That's funny, because the last thing you'd want to do when committing an act of sabotage is stomp around and get caught. It’s believed that sabotage came into use in 1910 as a noun, and then later in 1918 as a verb. Apparently, people only became so cruel in the last century or so.