The essay should stand on its own without the anecdotal catalyst (the fight). You can write the essay of your motivation without mentioning the event or at the most dedicating 1-2 sentences to it in vague terms.
Think of the examples that show how you have demonstrated the “motivation to succeed” What does success look like to you?
Specific examples of setting high but realistic goals. Actively seeking and taking advantage of opportunities. Being able to deal with setbacks or obstacles. Seeking and applying feedback to improve an outcome.