If i understand you correctly try this:
Make a table "Team" with id_team as a primary key Make a table "player" with id_player as a primary key set id_team as a foreign key in table Player
that way you can select all players who have id_team == lets say 5
select * from Player where id_team = 5
here is the database model if it helps: model
It is not recommended to store whole objects into Mysql databases afaik, you should consider storing just a simple data like players name, players age etc. Then after selecting those data, rebuild those object from selected values. But if you insist on storing objects here is thread : How do I store an php object in a MySQL table?