Helmet-to-helmet collisions are occurrences in American and Canadian football when two players' helmets make head-to-head contact with a high degree of force. Intentionally causing a helmet-to-helmet collision is a penalty in most football leagues, including many high school leagues. 
Despite its long association with American football, this type of contact is now considered to be dangerous play by league authorities due to the potential of causing serious injury. Major football leagues, such as the National Football League (NFL), Canadian Football League (CFL), and NCAA, have taken a tougher stance on helmet-to-helmet collisions after the US Congress launched an investigation into the effects repeated concussions have on football players and the new discoveries of chronic traumatic encephalopathy (CTE). Other possible injuries include head traumas, spinal cord injuries, and even death. Helmet manufacturers are constantly improving their designs in order to best protect their users against injuries from such collisions.
The crackdown on helmet-to-helmet collisions has resulted in reappraisals of the sport. An image of two helmets smashing together—which had been a staple for 20 years—was dropped in 2006 from Monday Night Football on ESPN. The NFL also ordered Toyota Motor Company to stop using a similar helmet collision in its advertisements.
Rules by league
- The Canadian Football League prohibits the use of the helmet to butt, ram, or spear an opponent. Players are penalized for what is not deemed to be an 'acceptable' football play.
- In the NCAA, helmet-to-helmet collisions have been banned for years, but they were illegal only when intentional. In 2005, the NCAA took the word "intentional" out of the rules in hopes of reducing these incidents even further. Beginning with the 2013 season, players who are flagged for such hits are automatically ejected from the game in addition to a 15-yard penalty, under the new "targeting" rule, subject to a replay review. If the ejection occurred in the second half or in overtime, the player must also sit out the first half of his team's next scheduled game. This rule was revised in 2014 to overturn the yardage penalty in addition to the ejection if the player's hit is not flagrant. The rule was again revised in 2016 to allow replay officials to call penalties if they were missed by on-field officials and overturn incorrect penalties.  The NCAA is currently proposing to modify the policy again to allow players to remain in the game if there is insufficient evidence for replay officials to confirm or overturn a call, but the 15 yard penalty would still be enforced. 
- In the NFL, helmet-to-helmet hits are banned, with a penalty of 15 yards for violations. In 2010, the NFL placed its policies pertaining to these incidents under review, considering heavy fines and suspensions. In 2017, NFL has adopted the NCAA's "targeting" rules, which will not only penalize players, but will review the play and automatically throw any offenders out from the game.  The first suspension under this rule occurred on December 13, 2011: James Harrison received a single game's suspension after such a hit caused Cleveland Browns quarterback Colt McCoy to suffer a concussion.
Opposition to helmet-to-helmet collision bans
Despite the safety concerns, in 2010, some professional football players criticized bans on helmet-to-helmet collisions on the basis that gridiron football is a game that is supposed to be composed of the world's biggest and best athletes, and placing such restrictions "waters down" the game.
- Concussions in American football
- Concussions in sport
- Health issues in American football
- Helmet removal (sports)
- Impact monitor
- Bounty Bowl
- New Orleans Saints bounty scandal
- Chronic traumatic encephalopathy
- National Operating Committee on Standards for Athletic Equipment
- "High School Football Rules Changes Continue Focus on Risk Minimization". www.nfhs.org. Retrieved 2018-10-11.
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- Garrett, Melanie (December 2010). Under His Helmet: A Football Devotional. p. 23. ISBN 9781617391743.
- Thomas, Katie (October 21, 2010). "N.F.L.'s Policy on Helmet-to-Helmet Hits Makes Highlights Distasteful". New York Times. Retrieved 9 December 2011.
- Bucholtz, Andrew. "Concussions: the CFL's rules and the impact on defensive players". Yahoo Sports. Retrieved 27 December 2011.
- Nowinski, Christopher (September 2006). Head games: football's concussion crisis from the NFL to youth leagues. pp. 104–05. ISBN 9781597630139.
- D'Andrea, Christian (March 28, 2017). "NFL officials just OK'd a rule that brings the NCAA's 'targeting' calls to the big leagues". SBNation.com. Retrieved 5 August 2017.
- Klemko, Robert (December 13, 2011). "Steelers LB James Harrison suspended one game". USA Today. Retrieved 13 December 2011.
- Gregory, Sean (Oct 22, 2010). "Can Football Finally Tackle Its Injury Problem?". Time Magazine. Retrieved December 13, 2011.