Dont slide with your spikes up
Ty Cobb is the first player that comes to mind for this unwritten rule. Many players from his era publicly complained of Cobbs tendencies to slide into bases with his spikes up, putting fielders in harms way. It is one thing to slide away from the bag to break up a double play, but deliberately trying to put someone on the disabled list is another. Karim Garcia broke this unwritten rule in the aforementioned scene in the 2003 ALCS, as did Shelley Duncan (left) in a spring training game on March 12, 2008, causing benches to clear.