A professional smasher, commonly shortened to pro, is a person who plays a Super Smash Bros game at a very high level of skill and often makes a living or acquires income from playing the game. In general, professionals regularly make money off of playing the game in tournaments and/or is recruited and sponsored by a notable organization, such as Major League Gaming or Cloud9. A professional is also commonly considered the person at the top of the metagame of that said character, such as Armada for Peach or Axe for Pikachu.
Other types of professionals
Semi-professional
A semi-professional, or a semi-pro, is a player with above-average skill who can rank high and win money in local tournaments, but lacks the overall prowess to place well at regionals and nationals.
Top professional
A top professional is a player who is among the very best from his country and/or for their respective main character. Notable examples include Mew2King, Anti, and Ally for Brawl; Mew2King, Mango, and Armada for Melee; and Isai, SuPeRbOoMfAn, and Jousuke for Smash 64. These players consistently place high at any tournament, and have the potential to win national tournaments.
Income and standard of living
Being a professional Smasher is widely considered to not very lucrative given the time commitment. In a Reddit post, Hungrybox speculates that Mango is the highest earning Smasher and earns $70,000 a year from tournament winnings, Twitch subscriptions/donations/ads, and Cloud9 stipend.
ZeRo revealed that he makes around $40,000 in 2014.[1] S2J said he used to make 1k+ a month from getting 1st-3rd at Super Smash Sundays/Mayhems.[2]