This shows a large rally held at Fenway Park in Boston in support of Irish independence. The photo was taken some time in the 1910s.
Source: Boston Public Library
President of the Irish Republic, Eamon De Valera, visited Boston in 1919 and was welcomed at Fenway Park by 50,000 supporters, possibly the largest crowd ever in the ballpark. The Boston Globe covered the rally in an great piece published on June 30th, 1919.