They're one of the most unfortunate parts of any sport. But since they happen in almost every single game, fans, players, coaches and front offices just need to live with them.
While it's always a little more solemn in a locker room following the news of an injury, when a player gets hurt by one of his or her own teammates, it's definitely more quiet.
We've seen guys bust their legs in celebrations and sustain a concussion thanks to a hit from their own guy, which is why I'm giving you some other injuries that came thanks to players getting blown up from their teammates.
This seems to happen nearly every season to a number of quarterbacks, but the Browns' Brandon Weeden is just the latest example of it.
While passing a football, Weeden's release caused his thumb to nail the top of his lineman's helmet, forcing him to leave the game and, as of right now, miss one game.
Helmets are worn to protect guys, but sometimes, that hard plastic can cause some serious hurtin'.
I'm guessing that this isn't the way this goalie drew things up, but, nevertheless, he just increased his goals against average.
After collecting the ball in his box, the gloved kid tried to quickly clear the ball, but instead nailed a teammate on the back of his head and scored on himself.
The ball didn't appear to knock the kid out, though you can be sure this was a double whammy for everyone involved.
Come on kid, don't you remember the five D's of dodgeball that Patches O'Houlihan gave in the movie? You've got to dodge, duck, dip, dive and dodge to be successful at the sport.
Obviously, this dude was either sick that day of class or just slept through that part of the instructions, because he got absolutely nailed by his teammate at point blank range.
Miami Marlins left fielder Chris Coghlan may have earned himself the 2009 NL Rookie of the Year award, but he would have never even been nominated for best celebration after this fail from back in 2010.
Trying to stealthily sneak up on teammate Wes Helms to smother him with a shaving cream pie after a walk-off win, Coghlan overshot the face smash, flying out of the screen and injuring his knee in the process.
Come on dude, you're not supposed to be the one getting knocked down while celebrating.
If you hear the train, get the hell out the way!
That's the message that this Lingerie Football League player had for her teammate as she tried to find the crease to fit through on a run play earlier this summer.
With girls scantily dressed and running around playing football, how come there aren't more guys going to these games?
There was a time in his career when third baseman Eric Chavez routinely earned himself Gold Gloves after every season—collecting six-straight in the early to mid-2000s.
But while he could make spectacular plays on scorchers coming his way at the hot corner, he seemed to have trouble with this throw back to his own pitcher last season, plunking Cody Eppley in the head.
Dude ended up OK, and, if you check the tape, at least Chavez was trying to give him a fair warning.
Maybe former Florida Gators safety Matt Elam was just jealous that he wasn't actually involved in the tackling of an LSU player, because he came in with a full head of steam on his teammate Loucheiz Purifoy to "celebrate" his take down.
The knock down might have been on his own guy, but I wouldn't have been surprised to see the refs through a flag for a late hit, because that thing was pretty solid.
It might not look like much, but Real Madrid goalie Iker Casillas' little brush up with teammate Sergio Ramos actually caused the netminder to come out of the match just 14 minutes into it.
There were no broken bones or real seriousness from the elbow to the rib, but it kind of shows that Casillas might just be a little bit of a sissy, don't you think?
At least he can laugh things off with Ramos.
It's a good thing that this kid wasn't playing in the NFL, because he no doubt would have received both a 15-yard penalty and a hefty fine from commissioner Roger Goodell for leading with his helmet.
As it stands, he just humiliated one of his teammates instead, letting loose a Ray Lewis-type hit that cause even his coach to fall to the ground.
Already with a suspect offensive line, the last thing the Steelers needed this year was to see their three-time All-Pro center, Maurkice Pouncey, go down with a torn ACL and MCL.
Injuries to big men happen all the time when trying to block behemoth defensive lineman. But Pouncey's was due to friendly fire, as second-year man David DeCastro rolled up under him, causing the leader of the line to get helped off.
OK, so this cannot feel good.
While trying to obey the rules of soccer by not grabbing the ball with his hands—though no one could blame him in this situation—this player tries his best to keep a loose ball from rolling across the end line for a goal.
To his surprise, a teammate comes in to try and clear the thing, catching a serious piece of the laying player's head, which, though an accident, probably cause some tension in the dressing room afterwards.
Never mess with the MVP of the league.
That seemed to be the message Capitals superstar Alex Ovechkin sent during a game this past May against the Rangers, when he chased after a loose puck and took out not just New York's Derek Stepan, but also his first-year 'mate, Martin Erat.
Erat slid into the net as if a train had just hit him, and was forced to leave with a hurt wrist.
We should all have a soft sport for a guy like Ravens wide receiver, Jacoby Jones.
After breaking out last season and displaying some killer dance moves during the Super Bowl, Jones' first game this year—where he was supposed to see an increased role with the team—ended when his own teammate, Brynden Trawick, ran into him accidentally on a punt return, causing Jones to sprain his MCL.
The injury has sidelined the wideout for the past few games, but apparently hasn't stopped him from getting injured in an alleged incident with a stripper and a champagne bottle.
Back when both were playing for the Celtics a few years ago, Paul Pierce and Nate Robinson almost had a celebration for the ages.
Not because it was a funny shimmy or dance that caught on with other players in the league, but because Lil Nate almost broke his neck when he jumped onto Pierce, getting flipped over and landing on the hardwood against the Knicks.
Standing at just 5'9", there are just some things little guys shouldn't try—and apparently, this is one of them.
Guys, how many times do I have to explain how to give a proper high five?
Stop just going for power on the thing—resisting the urge to slap the other hand with such force that it actually burns—and just focus on actually connecting on the thing by looking at the other person's elbow.
Apparently, Texas Rangers utility player, Jeff Baker, didn't know this, as he was actually put on the disabled list after spraining his thumb on a botched high five earlier this season.