Final answer:
Brant Barker demonstrates overconfidence or a lack of focus by showboating before scoring, leading to a fumble and the home team's loss.
Step-by-step explanation:
The character trait that Brant Barker demonstrates in the provided scenario is overconfidence or a lack of focus. Right before scoring a potentially game-winning touchdown, Brant indulges in a celebratory shuffle, which distracts him from the imminent threat of the opposing team catching up. This moment of showboating results in him being tackled, causing a fumble and ultimately leading to the home team's loss. It reflects a lapse in judgment and awareness at a critical moment in the game.