Do you think Xbox could sell better in Europe if it sponsored a big european football team?

That might help since Europeans do love football. I'm not sure how MS can fix the European sales situation. The only thing that can help them is FIFA exclusivity but that's not allowed. 

They would be better off sponsoring a League than a single team like the Premier League or the Bundesliga.

Xbox Ultimate Game Sale

"The Ultimate Game Sale offers the best deals of the summer with steep discounts of up to 40%-50% on over 70 games across Xbox One and Xbox 360. And if you’re an Xbox Live Gold member, you save up to 10% more. Get the deals only July 7 - 13, 2015 and download from Xbox Store."

https://youtu.be/5LEtNoEMkwo

They should sponsor UEFA Champions League instead of a single league of a nation.

Sony already sponsors the Champions League.

So with XB1 over 7mill in the US do you guys think that it could go over 10mill with Halo/Holiday push?

Gazprom, Heineken, Ford all sponsor CL

Well it hit 7mil on 18th April, So by end of june will take it to around 7.4-7.5 Mil. I think with the holiday line up and the Halo 5 push coming it should hi 10mil, sicne November + December alone will hit over 2.5+ mil.

Every time I see the CL there are PS4 ads on the field, CL has many sponsors but I'm sure that they can't have two sponsors that are in the same bussiness or offer the same product like both Coca Cola/Pepsi, Heineken/Budweiser,Ford/Toyota.