I say directly meaningless, because you may stand to gain or lose indirectly due to the outcome, if you have, for example, wagered money on it (for this post, I define gambling as the mental interest in a directly meaningless outcome over which you have no control, and wagering as the addition of something meaningful as an indirect result of the outcome; by meaningless, I mean that it has no meaning to you). The gain or loss from the wager is an indirect result of the outcome; the direct result is that the players go back to their houses and the ball gets put back on the shelf (i.e. has no meaning). In contrast, the winner or loser of an election, another event beyond your control in which you might have an investment, has direct, meaningful results, even if some of these results might not occur immediately.
Gambling is the mental investment in a directly meaningless outcome over which you have (or no longer have) any control. Rooting for other people playing a game is gambling: rewarding the brain for events beyond its control. You might know that some outcomes are more likely than others. You may have invested effort into raising or lowering the odds of these outcomes. For example, you may have trained your horse to run well or bought better equipment for your team. But once the die is cast, so long as there exists a possibility that either side might triumph (even against the odds), if you care about it, you're a gambler.
The outcome of a game is always directly meaningless (except, perhaps, boxing). If you see people rowing to see who can get to the far shore first, but getting there directly results only in the ability to claim victory, then caring about it is gambling. If the one who gets to the far side first avoids getting eaten by a shark, the result is not meaningless, and caring about it is not gambling: unless you don't care who gets eaten by the shark, in which case it is. You can always add a layer of meaninglessness on top of a meaningful outcome to transform it into a game. You change a competition into a game by adding the words "I win" to it. Succeeding in the competition is not "winning"; it's simply succeeding. The person who doesn't succeed could just as easily claim "I win" if she knows that the goal post is off the edge of a cliff.
When you become invested in the outcome of a game, or even the outcome of a single play, over which you are not exercising skill or talent, you are experiencing gambling. It's natural, because humans are wired for gambling. Even if you don't know who is playing, you want to see an effort rewarded (or punished) or a skillful performance succeed (or skillfully get opposed).
Why do people watch sports and gamble? Because we're wired to assess, but minimize, risks. Gambling provides the safest risk experience there is: we can experience, observe, and learn with no direct meaningful consequences. Wagerers (who bet money, etc) and players experience this risk more intensely, because they have tied real investment to their actions, making it a deeper experience and more primal; investing in the outcome is more educational and more productive.
Another reason we enjoy watching sports is tribalism, if we identify either with the participants or other onlookers; social connections are another primal aspect to being human. Yet another reason: escapism. Watching an event unfold over which we have no control is similar to reading or viewing a story unfold. So long as the game continues to capture our attention, we wonder what's going to happen next. This means that stories, plays, movies, etc also contain elements of gambling: we have a mental investment in a directly meaningless outcome over which we have no control. And we hope for a satisfactory conclusion.
Learning to gamble is a critical skill, exactly because it provides a safe space for evaluating the risks and rewards of taking chances, a skill that we use in non-gambling contexts throughout life.
The problem with gambling - when it is not tied to something meaningful, like wagering money - and sports watching is that it is time spent on something whose actual outcome is meaningless. It's fun: fun is necessary and even meaningless fun is often desirable. But other than sharpening out risk evaluation skills, it doesn't produce anything tangible. That same time and interest could be invested in research, science, creation, developing talent, developing your mind, participating in games where you have control (and thus are gaining or utilizing skills), and any number of other useful activities, many of which also sharpen our risk taking skills in a relatively safe way. Again: some mindlessness can be therapeutic, but it's not the best choice for all or most of the time, even leisure time. It is, after all, lazy.
