Reiver_2016

Morning guys. I am quite new to this game and mostly playing in tier 2 and 3 matches. Sometimes we get totally stuffed and in these games I noticed that the opposition had a good number of players with the letter A or B after their names. Are these pro players, what does this mean? Equally when we do well , we sometimes have these players in our team! It may well be coincidence but I am interested to find out. Thank you .