/Scoreboard teams add/remove command doesn't work correctly with @p , @r
It will team with name @p , @r , @r[x=5,y=6,z=7] etc.
Unless you specified the c=<number> filter and <number> is not equal 1 ( -1 , -5 , 0 , 5 ,12 etc.)
Example
There is 5 Players in your server
/Scoreboard teams add/remove @p – it will add/remove the team named '@p'
/Scoreboard teams add/remove @r – it will add/remove the team named '@r'
/Scoreboard teams add/remove @p[m=2] – it will add/remove the team named '@p[m=2]'
/Scoreboard teams add/remove @p[m=2,c=1] – it will add/remove the team named '@p[m=2,c=1]'
/Scoreboard teams add/remove @p[m=2,c=2] – it will add/remove the team with name of 2 Player that is in Adventure Mode
/Scoreboard teams add/remove @r[c=2] – it will add/remove the team with name of 2 Random Players

Sorry for my bad english