Fill in the blank with the correct option.

A small ______ between two children ended up as a group fight

The correct option is altercation.

Here is a step-by-step explanation of why this option is correct:

1. Analyze the context of the sentence: The sentence describes a situation where something small between two children escalated ("ended up as") into a "group fight". This indicates that the blank must be filled with a word that represents a minor disagreement, argument, or dispute.

2. Evaluate the options:
- altercation: An altercation is defined as a noisy argument or disagreement, especially in public. A "small altercation" between two children fits perfectly as a precursor that could escalate into a group fight.
- match: A match usually refers to a sporting event or a game. While it involves competition, it does not inherently imply a disagreement or fight.
- contest: Similar to a match, a contest is a competition to do better than others. It is usually organized and rules-based, rather than something that naturally escalates into a group fight.
- race: A race is a competition of speed. It does not fit the context of escalating into a fight.

3. Conclusion: Therefore, "altercation" is the only word that logically connects a minor disagreement between two individuals to a larger group fight.