The phrase "first teamers" refers to the main or starting players in a sports team. They are the ones chosen to play at the beginning of a match or game. Full definition
At his age, ramsey and wilshere were regular first teamers for Arsenal. (justarsenal.com)
It was becoming a bit worrying with the number of Arsenal stars that were not going to be fit for the start of the season, but at least we can be hopeful that our star man Alexis Sanchez will be able to link up with other first teamers for the opening game against Liverpool. (justarsenal.com)
In the mean time I guess we'll just have to hope that our current crop of first teamers work on their defensive duties in training. (justarsenal.com)