The description that best fits the characterization of Mr. Pearson is He is tired of Squeaky dominating the race.
This is evident from the following passage:
"Come on, Squeaky," Mr. Pearson said. "Give someone else a break this year."
He shook his head sadly and went back to his clipboard.
Mr. Pearson's suggestion that Squeaky "give someone else a break" implies that he is tired of seeing her win all the time. He also seems to be hopeful that the new girl, Hazel, will be able to challenge Squeaky and offer a different outcome to the race.
The other options are not supported by the text. While Mr. Pearson is organized and exacting, he does not seem to be particularly enthusiastic about the race. He also does not seem to have any personal stake in the outcome, as he is not cheering for any particular runner.
Therefore, the best description of Mr. Pearson is that he is tired of Squeaky dominating the race and is hoping for a different outcome.