run across

informal

to meet someone you know when you are not expecting to:
I ran across several old friends when I went back to my hometown.
(Cambridge Advanced Learner's Dictionary & Thesaurus からの run across sb の定義 © Cambridge University Press)

ビジネス英語
to meet someone without planning to:
After a couple of hours, I finally ran across someone who could help me.
(Cambridge ビジネス英語辞典 からの run across sb の定義 © Cambridge University Press)

- Cambridge Dictionary