According to Merriam Webster's, a sport is defined as "a physical activity engaged in for pleasure." I searched multiple reference materials and found similar definitions. "An athletic activity requiring skill or physical prowess and often of a competitive nature," said another.
I mostly agree with these definitions. A sport to me is definitely something physical, something that you have skill in, and it's something competitive in nature. I am going to mention some of the many sports that some people might not consider to be a sport in the first place.
First of all, cheerleading and dance are definitely sports. They both fit the definition. My girlfriend of five years has been a cheerleader all her life and I can tell you first hand that cheerleading requires a tremendous amount of skill and athleticism. And I'm not just saying this because my girlfriend told me to.
The amount of physical training and practice these athletes go through is incredible. You have to be in top physical condition. Strong enough to hold other humans up in the air is not easy. You also have to be flexible, and willing to get hurt.
Cheer is actually a pretty dangerous sport, being that they don't wear any pads or helmets of any sort. My girlfriend is a flyer and she has had minor concussions and other numerous injuries.
And as far as competition, competitive cheerleading and dancing teams compete in numerous competitions and tournaments against other teams, usually by displaying and perfecting a vigorous routine. There are national and even world competitions.
This brings me to marching band. I played on the drumline for my university's marching band for all four of my college years and believe me, it's physical. We had to practice for almost two hours every day out on the field during the season. Constantly marching around and playing an instrument at the same time is hard work and it requires a lot of skill. We were required to play and compete at numerous marching band competitions, exhibition shows, etc. All of this considered, marching band definitely fits under the definition of a sport.
Even though I do classify a sport as something physical, I didn't forget about the sports defined to some as mind sports. This usually involves an activity or a game that requires more mental skill than physical. Some examples include chess, poker, and even video games.
I am a huge nerd at heart, and am a big video gamer. Video games are not sports per se, but there is a huge world of competitive video gaming that involves players training all day, every day in order to be able to compete in tournaments all across the world. It's called esports, or electronic sports. Some players even play video games for a living.
There are organizations such as Major League Gaming or MLG, who host major events where players around the world compete for cash prizes. Most events even include casters of the games, just like in other sports. One of my favorite video games to play is called Starcraft, where you build and control an army and have to defeat the other army. Games like this require an immense amount of skill and strategy. You have to be fast, multi-task well, and have great mental focus. It's not really physical, but it's funny because ESPN shows MLG coverage from time to time, which is awesome.
In conclusion, there will always be arguments over what's considered a sport. But to me there are simply two kinds, physical and non-physical. Either way, a sport is way of showing the world your passion and skill of a hobby, while having fun too. If you have a passion for a certain sport, keep doing what you're doing and don't let anyone tell you otherwise.