Just to add to this.
There are times you might have a young green flag player who is eligible to be picked up on waivers and put on your MLB roster. The reason being, they got called up to the MLB for a cup of coffee and have played in a game, then they were sent back down.
When you click on the player, there is a drop down tab to the right and tabs that say stats, games etc. Click on the games to see GP MLB. If still not clear, just go to Baseball reference and see if you see any GPs on the MLB club.
Again, if a player has zero MLB games, don't claim them off waivers or you will get a waiver wire penatly. Jim allows no errors for newbies since I guess he was not given leeway in some other league..