Wiktionary
phr. (context colloquial English) An implied conflict is starting.
Wikipedia
"It’s On (Move to This)" is a single by New Zealand R&B group, 3 The Hard Way, released in 2003. The single entered the New Zealand singles chart at number one and was certified gold.
"It's On" was the second single released from Naughty by Nature's third album, 19 Naughty III. It was released on June 8, 1993 and was produced and written by the three members of the group. The single found decent success on the Billboard charts, making it to 74 on the Billboard Hot 100 and 48 on the Hot R&B/Hip-Hop Songs. The song sampled jazz artist Donald Byrd's "French Spice" for which he received writing credits. The official remix was produced by the production duo, The Beatnuts and was featured on the B-Side of the single.
Usage examples of "it's on".
Make sure it's on the eastern grounds of the park, where the terrain is open.
I'm certain his Simnian delegation has also been indulging in bribery but I can't imagine it's on anything like the vast scale of corruption wrought by Tilupasis on behalf of our city.