it says -8.7 in red?

the games achievement say negative 8.7 in the details and points area on the achievement info page, what does that mean?

That means in whatever timeframe that chart is for (I think you can pick how many days) the score has gone down by 8.7. TrueScore is a constantly fluctuating number, and this lets you see that.

thanks boy this site does a good job on stat tracking

Yea, been on the Xbox side for years, looking forward to where this one goes. It's not perfect, but even now it can't be best in most areas.