The Gamemakers manipulated the Tributes' movements with the wall of fire in Chapter Thirteen.
Explanation:
The Gamemakers planned to use the fireballs to decrease the distance between Katniss and the Career Pack, or kill her if absolutely necessary. The reason why is because Katniss had ventured too far from the rest of the tributes and isolated herself, and so the gamemakers decided they wanted to bring her closer to the others with the wall of fire.
