The Anti Doping Agency has authority over chess. Their job is to monitor athletes for performance enhancing drugs. And with that you can drop the mike.
How do I defend the arguement that chess is a sport?

Chess is not a sport it is a game you cant just play chess you must play other sports at the same time to be successful at chess
A sport requires physical exertion, there's none in chess.
Therefore it's just a game, a prearranged game, he who studies more, wins.
Even within sports there's two categories, skilled sports such as football, cricket, tennis, Golf, Basketball etc, then there's endurance sports, no skill but a lot of physical exertion and stamina, not much else, marathon running, Cycling etc.
Unless you are a professional in a skilled sport, then you're not really proper, bone fide sportsman.
Sitting down at a table and pushing wood, is never going to be considered a sport, not by the dictionaries definition, not by any intelligent person's definition, accept it, and move on.

A sport requires physical exertion, there's none in chess.
Therefore it's just a game, a prearranged game, he who studies more, wins.
Even within sports there's two categories, skilled sports such as football, cricket, tennis, Golf, Basketball etc, then there's endurance sports, no skill but a lot of physical exertion and stamina, not much else, marathon running, Cycling etc.
Unless you are a professional in a skilled sport, then you're not really proper, bone fide sportsman.
Sitting down at a table and pushing wood, is never going to be considered a sport, not by the dictionaries definition, not by any intelligent person's definition, accept it, and move on.
Ok, I recognize that I'm biased here, but I disagree. Endurance sports take quite a bit of skill in order to become good. It may not be inherently obvious, but a lot of effort goes into maintaining proper running form, breathing, posture, etc. The mental part of this also cannot be ruled out. The strategies that one uses during a race, the sheer willpower it takes, etc.

Modern technology has stripped away nearly all the physicality of chess. It's mostly a touchscreen game for devices, these days ... All you really need to do is tap or drag your index finger ...

Chess is not a sport it is a game you cant just play chess you must play other sports at the same time to be successful at chess
LondonWall wrote: A sport requires physical exertion, there's none in chess.
Sitting down at a table and pushing wood, is never going to be considered a sport (..)
a) A game can be a sport, and we can just play chess like we can just play tennis.
b) We need not be successful at a sport to engage in it. Being in overall good physical shape helps our brain bring in all its chess stamina and agility by means of a holistic flow, but if we are out of shape still our brain can be well trained, concentrating in a perpetual flow. This flow then will not last as long as it would in a fit body: Our physical organ brain will tire earlier from its physical exertion of playing chess if supported by a not very fit organism.
c) But if you want to say mental fitness and mental exhaustion are not physical, okay, where are you at? If awareness and responsiveness are not physical, alright, what are they? There is a difference between muscles and neurons. But holding concentration is a little like holding a weight, and juggling balls is a little like keeping several chess motives afloat, playing a position. They are all talents, they are all givens- bodily talents, bodily givens- that can be trained and shaped.
d) What is won by not calling pushing wood sport? You cannot see the brain activity in the moving hands, a mindless move and a worked out one can look the same. So, it's kind of a black box sport. But we know it's sport, 'cos we know the black box ain't empty. And that the vocabulary we use for describing the action in our brains is that of sport: demanding training, multi-faceted exercises, hard work.
e) Why is doing maths no sport? Well, it can be sport- like chess, it can be pursued as a job, as sport, as leisure. Visiting the etymology, French 'desport' meant engaging in divertissements, amusements. And let's remember Wittgenstein, concepts like 'games' or 'sports' would be fuzzy balls of wool held together by family resemblances, not by definitions.

even if it makes them feel good, it is not a sport no matter how bad they want it to be a sport. A sport is played outside and involves movement and not just looking at a board of pieces and thinking about where to move them. You have to actually be moving around.

even if it makes them feel good, it is not a sport no matter how bad they want it to be a sport. A sport is played outside and involves movement and not just looking at a board of pieces and thinking about where to move them. You have to actually be moving around.
Completely agree. I've heard lots of claims that some chess players consume a lot of energy playing chess and even lose weight during the course of a game, although it's hard to fathom how that could happen.
Psychological stress and inactivity. This kind of stress negatively impacts the gut, and is the opposite to fitness.
1) it's a relatively meaningless semantic argument that in my experience boils down to: "but the thing I do / like is hard / tough / to be given respect too!"
2) if the point is to prove that chess is hard / tough / to be respected for the effort involved, it's an uphill battle to compare it to 'sport' in terms of how gruelling it is. You're accepting the bait and arguing on their territory. Talk about mental toughness and processing speed, etc - that's the bit that 'sport fans' see as elite and chess players are best at. Anyone's favourite athlete "sees the game differently", "has eyes in the back of their head", "is two steps ahead of everyone else", "is playing chess while everyone else is playing checkers", "is tough under pressure", "never gives up", etc.
3) For a group arguing about mental acuity, there sure are a lot of people backing up this argument from an early post:
"First and foremost, it is important to consider the definition of a sport. The Oxford Dictionary defines a sport as “an activity involving physical exertion and skill in which an individual or team competes against another or others for entertainment.” While chess may not involve physical exertion..."
Whatever arguments you want to make, that's not where to start.
Chess is not a sport, it's largely a prearranged game, all of the end games and all of the openings have already been completely worked out for you, it's just a matter of studying them, it's only the middle game that can claim any kind of creativity but even then a computer can work out the best move, you cannot use a computer to determine the outcome of real sports that actually involve physical exertion and split second decision making. This is not even a debate, it's laughable nerds and geeks are trying to make out they're sportsman
You can talk about this all day long every day, but the vast majority of people are never going to accept sitting on your arse, hitting a clock and moving pieces of wood is a sport. Get over it.
I have classmates who disagree about this... What are the best arguments you guys have?
Why is there a need to settle the disagreement among classmates? Let them argue while you go play another game of chess.