up and at them
1. {adv. phr.}
Actively engaged in a task as if doing combat.
"You want to know whether he will make a diligent worker?" Dick asked. "Well, I can tell you that most of the time he is up and at them like no one else I know."
2. {v. phr.}
To become aggressively engaged in doing something; (useable as a command).
Come on, up and at them, you guys. We still have a lot of work to get done.
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Source: A Dictionary of American Idioms