Relative clauses (連体修飾節/関係節) that have more than one possible interpretation, like 紹介する人.
Japanese relative clauses work by pulling out a noun to be modified and removing the accompanying particle (が/を/に/へ/etc). This sometimes results in ambiguous relative clauses. They typically happen when a verb takes two or more human arguments (e.g., AがXをBにあげる, AがBをCに紹介する, AがBを好きになる, AがXをBに食べさせる):
プレゼントをあげる人
- the person who gives the present to someone (the giver)
- the person who someone gives the present to (the receiver)
In relative clauses, は becomes が, which is another source of ambiguous relative clauses:
太郎が好きな人
- someone who likes Taro
- someone who Taro likes
This tag is for questions around this problem.