Complex sentence: Blackpool began the campaign on 4 September, 1915 with an away match at Southport Central, which they lost 2--0 in front of a crowd of 1,100 (when attendances were recorded during the war years they were often estimated).
Split into simpler sentences: Blackpool began the campaign on 4 September, 1915, with an away match at Southport Central. The visitors lost 2--0 in front of a crowd of around 1,100 (attendances recorded during the war years were often estimated).