I don't know guys, here's what one person has to say.
On the other hand, I too feel Nike runs small (or one can say Adidas runs big

)
I think I can explain why he feels like that about the Adidas shoe size compared to the Nike shoes size.
He's from the UK and he says everyone he knows in his tennis club in the UK feels the same way about the shoe sizes - Adidas runs smaller than Nike - the complete opposite compared to what people form the US feels like.
I'm from Europe, but I always buy based on US sizes and not UK sizes, because I buy most of my golf and tennis gear in the US.
If you looke at the specifications for for instance the Adidas Barricade V and the Nike Breath Cage II shoes and compare the US and UK sizes, you will undertand the reason why people from UK feels the totally opposite as to what people in the US feel about the Adidas shoe sizes.
I use a size US 13 in Nike shoes - and this is a fit on the slightly tight side, and an Adidas Barricade size US 13 therefore fits me a little less tight and more comfortable - but both are OK. I like a tight fit, when I play tennis, so Nike US 13 is perfect, but Adidas US 13 is also OK, but a little on the 'loose' side.
Inside my Nike Breath Cage it says US size 13, but UK size 12 and EURO 47.5.
But, and this is the reason why people from the UK feels this way about the Adidas shoe fit inside my Adidas Barricade V, it says US size 13, but UK size 12.5 and EURO 48.
So if I was a guy from the UK buying a pair of Adidas shoes, and I fit into a Nike size UK 12, I would just get an Adidas Uk size 12 also. But an Adidas UK size 12 is the equivalent to a US size 12.5, and NOT a size US 13.
So the UK guy feels like he needs to buy ½ size larger to get the same fit as the Nike shoe, he normally buys in the UK.
A guy from US won't understand this, because he of course always buys based on the US shoe size and NOT the UK shoes size. Adidas and Nike translates the shoes sizes from US to UK in slightly different ways and this is what makes the UK feels the Adidas runs small in size and while the US guys feels like they run on the larger side compared to a Nike shoe.
Hope you get my point :lol:
Check these two pages out:
http://www.tenniswarehouse-europe.com/descpageMSNIKEH-NBC2WBR.html
http://www.tenniswarehouse-europe.com/descpageMSADIH-AB5WBS.html