There was an enormous amount exciting action during the National Football League’s opening week. Unfortunately, there were also teams whose plans changed unexpectedly and drastically after the games played. Many ball clubs around the NFL suffered devastating injuries to key players.

The San Diego Chargers were the first team Sunday to have a key player go down. Wide receiver Keenan Allen went down with a non-contact knee injury as he came out of a break on a passing route.

It was a very tough injury to watch. Allen has worked extremely hard this offseason.

The wide out had six catches for 63 yards in the first half after missing the last eight games of 2015 with a lacerated kidney. Allen tore the ACL in his right knee Sunday and will miss the remainder of the season.

Cleveland Browns quarterback Robert Griffin, III was looking to resurrect his career in the NFL this year but had his journey cut short. The 2012 first-round draft pick suffered an injury on a hit he took on the sideline at the end of a run and has a fractured coracoid bone in his left shoulder. The team placed him on IR (now eligible to return) and he could be out for the season.

One up-and-coming cornerback with the New Orleans Saints, Delvin Breaux, broke his fibula in the second quarter of the team’s matchup against the Oakland Raiders. Breaux tried to play through it and was eventually carted to the locker room. He is expected to miss six weeks.

Houston Texans linebacker Brian Cushing was carried to the locker room in the first quarter with a knee injury. The 2009 Defensive Rookie of the Year has missed significant playing time with a plethora of injuries in both 2012 and 2013. He could be out for six weeks with a torn medial collateral ligament.

Professional football is a violent game and injuries are part of it. General Managers and head coaches know this. And every ballclub makes a valiant effort to put together a roster that is full of talent so that when those injuries hit, there isn’t a huge drop-off in the quality of play during contests.