Examples:
Friend 1: If I'm a specialist in Chinese Football League and i follow all matches, news, statistics etc. I have a strong knowledge of it and I'm trying to predict a score based on very strong information. Than I decide to put 100$ on the match.
Friend 2: Goes to the casino. Sit by the roulette table. Chose a number and put on it 100 $.
Who is the gambler?
Gambling is a relative term. It means different things for different people. For Friend 1, some may consider that gambling and some may not. Friend 2 is definately considered gambling .
these both are the gamblers, as these both are gambling with two different gambling types, sport betting is one type of gambling and playing on casino is another type of gambling in both they bet the money.