In Standard leagues there are going to be many unclaimed players available in the player pool; these players are called free agents. You may want to pick up one of these free agents (players not currently on a team in your league) to improve the strength of your team roster. You can search the player pool by going to the Players page.
All Standard leagues will observe ESPN's Undroppable Players list. The Undroppable Players list is comprised of select elite level players who cannot be dropped to waivers at any time during the football season.
NOTE: If you wish to claim a player from free agency, you must have an open roster slot or drop one of your current players in exchange. Only LM leagues can modify the undroppables list (and only the League Manager can do so by going to the LM Tools tab and clicking on Edit League Settings, then clicking "Edit" next to Player Rules and then selecting "No" next to "Observe ESPN's Undroppable Player List).