I've seen this before on a few journal's but here's a rough idle just off googling :o

Art Fight is an annual art game that lasts for 1 month. Users can register on the site to join in. Each year, participants are split into two teams to which they are assigned randomly. Players "attack" people of the opposing team by making art of original characters you choose belonging to members of the other team.

I had been seeing quite a bit of this too lately and wondering the same thing; so I searched and found - this - which seems to explain it fairly simply.

Art fight has its own website as well as some other platforms advertise and manage art fight too. Its basically free art yet behaves like art trade. Every time a member of the team "attacks" with art, that team gets points. I'm never in them so idk how the points work towards at the end, however I assume it would correspond with the platform its on.