were
Grammatically, England was poor yesterday, is actually the correct version. 'England' is not a plural. To say, England were poor yesterday, you would have to say 'the England players'.
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England (national team) is plural.
England (as a country) is singular.
England were struggling to hit the ball off the square...
http://news.bbc.co.uk/sport1/hi/cricket/england/6287095.stm
The disappointing thing was that England were absolutely cruising until Holland...
http://news.bbc.co.uk/sport1/hi/football/internationals/6152906.stm
England were booed off at full-time...
....etc etc etc