Both are fine.
The team were overwhelmingly defeated in yesterday's game.
The team were defeated overwhelmingly in yesterday's game.
which one is correct?
Both are fine.
"The team was..." in AmE.
It can be 'was' in BrE, too, but it doesn't have to be.
*NOT A TEACHER* I agree - both are correct. But I believe the first emphasizes the verb (defeated), while the second seems to emphasize the adverb (overwhelmingly.) One other point, if you are interested: The auxiliary verb (were) does not agree in number with the subject (team). "Team" is singular and the correct (singular) form of the verb is "was" - not "were."
*NOT A TEACHER* I offer my sympathy to saloom2. Not only is he/she trying to learn English, but runs into these contradictory differences between accepted British and American English from well intended persons from both camps. For some this type of contradictory information must be bewildering rather than helpful. I'm a newbie, but it already seems to me that the majority of the teacher responses are from those who probably prefer to use BE rather than American. Would the forum serve better if Americans didn't offer our understandings?
Some of us, speakers of both AmE and BrE and of other varieties, need to remind ourselves sometimes that what is absolutely true in our variety may not be so absolutely true in another variety. Learners generally cope well with the different varieties, and learn to pick what suits their needs best. The only times when problems arise is when one of us insists that our variety is right and the others are wrong.
For some reason, the majority of the people who respond regularly in this forum happen to be from the British sector. This doesn't matter. Some of our most valued gurus are American and Australian, and they help ensure that this forum provides a balanced view of English. We also have valuable input from speakers of other varieties of English, and from non-native speakers (some of whom give more helpful responses than some native speakers do).
So, as SoothingDave wrote, all are welcome.