Certain outdoor sports have acquired a reputation for their exceptionally high level of difficulty. Members of a popular online forum identified the sports they believe fall under the category of “the hardest sports.”

1- Ice Hockey

A sport where literal fist fights are just as part of the game as its techniques should come tops on this list. A sport played on ice between two teams of eleven players each. The game's object is to get the puck, a small, hard rubber disk, into the goal of the opposing team.

How the players balance their weight on ice while dribbling through opponents at the speed they do isn't for the faint-hearted. 

2- Boxing

To throw fast, hard, and precise blows for 12 three-minute rounds of boxing, you must have lightning-quick footwork and the ability to deflect blows from an opponent trying to knock you out. It implies that endurance and mental toughness are necessary to compete in the boxing ring. It also means that physical strength is required, as is the scientific use of that strength. The possibility of a boxer suffering a life-threatening injury is relatively high.

3- Rock Climbing

Climbing takes a high level of technical proficiency and an almost unmatched degree of mental focus and independence. Unlike other activities, climbing requires physical fitness; one can have it or not, depending on the pitch, challenge, or route. And if they don't, the results might be fatal.

4- Mixed Martial Art

Combining the trio skill of boxing, wrestling, and martial art, this extreme combat sport is scary. It is a total-contact combat sport that combines tactics from several other combat sports worldwide. It is based on striking, grappling, and ground fighting that often leaves the loser injured, accumulating the highest injury incidence rate amongst other full-contact sports.

5- Swimming

In the aquatic sport of swimming, athletes try to swim as swiftly as possible while employing different strokes such as the Butterfly, Backstroke, Breaststroke, and Freestyle. Some people can find swimming to be a relaxing afternoon activity. Others view it as a sport requiring extraordinary power and stamina. Swimming is either regarded as one of the most physically taxing sports or one of the most calming sports, depending on who you ask.

6- Mountain Biking

Like climbing, mountain biking demands high technical proficiency, bravery, and talent. It also has a high entry barrier regarding skill requirements to navigate a downhill course successfully, and the consequences should one take a wrong step are severe. Although riders enjoy the help of gravity, being a good downhill rider does not require a high level of aerobic fitness.

7- Car Racing

This user couldn't put it any better: “Keeping 100% focus throughout, at speeds faster than most people can react to. Not to mention constantly adjusting the setting on your car and adjusting the brake balances.” Given the zero margins for error, it takes a particular sort to defy G-forces with their drifts through the circuit, speeding their way toward the checkered flag.

8- Water Polo

While polo resembles hockey (hockey is played on horse-riding), water polo is likened to handball (handball is played in water). Treading water while holding the ball in attack or being drowned to be dispossessed is lunacy only the brave dares. The necessity to avoid drowning is the most challenging aspect of this game, giving it its jump in technique level.

9- Gymnastics

Evolving from the exercises used by the ancient Greeks, gymnastics is a complex sport that demands physical strength, flexibility, grace, agility, power coordination, balance, and control. The mental finesse to harness all these qualities for a perfect performance validates this sport on this list.

10- Rugby

Imagine teams piling into a “ruck” and competing for the ball rather than having the game stopped at each tackle. Akin to American Football (which uses protective gear), rugby is arguably the most dangerous contact sport globally since it requires much endurance and fitness.

A player must sprint across a large circular field while dodging tackles from his ten fellow teammates. The main objective of this game is to prevent the opposition from scoring. As a result, kits and unintended blocks are standard in the sport.

11- Ultrarunning

The prerequisite for beginners belies the tremendous challenge of this sport that covers a hundred miles. To qualify, a newbie must have accumulated 26.2 miles or more, thus requiring about four times the effort and technicality to finish the grand race. Dealing with the in-game challenges of dehydration, sore feet, cloudy eyes, and strained muscles equally takes an emotional toll that not every participant finishes.

12- Skiing

It calls for the stamina of ultrarunning, the sprinting quickness of mountain biking, and the mental fortitude of open water swimming, and, occasionally, it can place skiers in circumstances of genuine exposure. Athletes must maintain unmatched cardiovascular fitness in addition to muscular strength and coordination if they are to succeed.

13- Motocross

We have hardly overcome the fear of riding on four wheels, much less taking leaps and ditches on two wheels on winding roads across undulating terrain. The handlebars attached to control speed and direction do not make the high jumps and dangerous landings any less daring, making it one of the world's most challenging and physically taxing sports.

14- Skating

Shattered bones, dislocated joints, and fractures. Nothing will if these injuries do not convince you of the precision required in skating. The athletic execution required (speed, grace, and balance) for the flings, hops, and other footwork must be adequately synchronized to transmit the skater's weight on 4mm thick ice and to avoid the spoilers of a bad fall. Otherwise, it is “career over.”

15- Soccer

The principal opinion on this significant tool for social change is that it is an easy game to learn with skills that are difficult to hone due to its physical demands, especially with the recent evolution where every player must adapt and contribute to the attacking and defensive phases of the game.

The emotional aspects extend to worldwide expectations of fans, given the sport's worldwide appeal. Have you noted the aura during penalty shootouts? You dare not miss it.

16- Football 

Need we say more? The risk of injury in football, from broken bones and concussions all the way to cardiac arrest, makes it incredibly dangerous. The NFL has made strides in recent years to protect its players, though many believe these interventions are too little, too late. 

Source: (Reddit).