Player forget to put battlefield and draw first hand

The battlefield is placed now and the game continues — it's a fixable setup error, not a restart.

Forgetting to put your battlefield into the Battlefield Zone makes your deck's presented contents illegal, which is a Deck Presentation Error [Warning] (TR 703.4). The remedy is straightforward: place the selected battlefield face-up in the Battlefield Zone — it's public information and was never shuffled into your deck, so nothing about the opening hand or mulligan is affected (TR 703.4.c.2; CR 113, 170.2). Battlefields are established at the start of the game and must remain in play (CR 170.2.b), so the game can't proceed without it. Note: at high OPL, if the opponent catches the error after hands are drawn, the penalty can upgrade to a [Game Loss]; at casual/regular events, a judge will just fix it and warn.