Two familiar functions of grammar in all languages are pronoun reference and plurality.

Note the shifting singular-plural in the following passages describing conquests:
1. And Israel, they [plural] struck him with the edge of the sword,
2. and he [Israel, singular] conquered his land from Arnon to ....
3. ...
4. And Moses sent to spy out Jaazer,
5. and they [plural - the spies] took its villages,
6. and he [singular - Israel] conquered the Amorites who were there.

We have embedded the grammatically natural Rashi comments in the translations above. Note the grammatical rule on the difference between attacks and conquests:
• When conquests are stated in the singular they indicate a unified war attempt by a country;
• WHen attacks are stated in the plural they indicate a multi-flank attack, with each flank acting independently.
Hence
• The attack indicated in bullet #1 above is plural to indicate a traditional multi-flank war attack
• the conquest indicated in bullet #2 indicates a united military effort
• Similarly the conquest indicated in bullet #6 indicates a united military effort.
• But the plural in bullet #5, to indicate a conquest, looks peculiar. Hence Rashi refers the plural to the spies. Simple but to the point.

Advanced Rashi: Rashi adds: The Jews learned their lesson from the first spies who insulted God. These spies had faith in God to help them conquer. They in fact conquered the villages.

We can use this to show a fundamental fallacy in reading Rashi. Many people erroneously assume that Rashi wanted to illustrate a moral point - the contrast of the previous spies with the current spies and this moral point drove Rashi to make the comment that the spies conquered the villages. But we have done the reverse. We have correctly shown that the Rashi comment naturally emanates from a grammatical point and the moral point emanates from the grammatical point. This - basing Rashi on sound methodology such as grammar and inferring moral points after the Rashi comment is made - is the proper approach to Rashi. It also makes the moral points more believable.