Why do you receive a 404 when trying to visit Default.aspx on your SharePoint Site ( among other multiple reasons) ?
Answer ( among other potential answers )
The site might reside at the root of a Wildcard inclusion managed path.
Managed Path at /ManPath/
The Default page at http://SharePoint/ManPath/Default.aspx
When you try to access the site, you receive a 404 (Page not found)
Remove the managed path through UI or powershell
$wa = Get-SPWebApplication -identity http://SharePoint
How do you end-up in this ?
Well, by creating a managed path at the same URL as your newly created TeamSite