In his younger years R' Elazar Shach served as a Rosh Yeshiva in Stollen. How did a litvish gadol become a Rosh Yeshiva in a Chassidish yeshiva?
There was once a rabbinic conference in Lithuania, where gedolim, Admorim, and others were gathered. Suddenly, Rav Shach, who was a young avreich then, charged in. He had been closely connected with R' Chaim Ozer Grodzinski, and in their final exchange a question had remained unresolved. Now that Rav Shach had developed a clear answer, he felt compelled to share it with Rav Chaim Ozer immediately.
Some of those present protested, questioning the appropriateness of interrupting such a formal assembly. But Rav Chaim Ozer responded after hearing from Rav Shach and explained the situation: this young man, he said, is someone for whom nothing else exists in the world when he is engaged in Torah. The Stollener Rebbe, who was present, remarked that if this is his level of absolute immersion in Torah, then Rav Shach should serve as a Rosh Yeshiva of my yeshiva.
