Check your 'Control and Auto-Play Settings' screen on the Manager tab. If the manager won't let you, the option to control them will be disabled.
When hiring a new manager, you can tell whether they'll let you or not from their profile. The first option on the right under Game Strategy is "Lineup + Pitching Staff". If it's red, they won't let you touch it. If it's green, they will.
Pretty sure this is determined by their reputation (higher rep = wants more control) and their personality ('Controlling" = wants more control even at lower rep).
Edit: Boo, beaten to it.

And I'm pretty sure the Lineups icon on the manager page is new to '17.