Recently, a SWAT K-9 bit a SWAT officer during a building search and the injury required plastic surgery. To their credit, this team brought in expert K-9 trainers to ensure something like this doesn't happen again.
Years ago, a similar "friendly bite" occurred in another department during a drug raid. A SWAT officer was bitten by a non-SWAT K-9 during the entry. The SWAT and K-9 units had never worked or trained together prior to the raid.
Another search entry turned tragic when an officer accidentally shot his leashed K-9 partner. The devastated officer rushed his K-9 partner to an emergency vet clinic; however, not in time to save him.
One of the most tragic K-9 incidents of all happened recently in Florida. During a pursuit, a patrol vehicle struck and injured a K-9. Then, when the handler attempted to arrest a suspect, his K-9 partner bit the handler on the arm - refusing to let go. After repeated attempts to free himself, the handler was forced to shoot and kill his injured K-9 partner.
As tragic as the above K-9 incidents are, I want to point out that these are the rare exceptions to the rule. The overwhelming majority of police K-9 incidents have positive, uneventful outcomes. And police K-9s have proven themselves fiercely loyal, highly effective assets on countless occasions to LE agencies throughout the world, including the U.S. and Canada.