Assigning ownership of your own modifications to them seems significantly stronger than forbidding redistribution of your modified version. With this, just getting the examples to run on your own machine is effectively free development for the authors.
IANAL, but I don't see why this would not hold up. It is their code, its in their license agreement (which is a contract you agree to). If you do not wish to give them the rights to your modifications, the license forbids you from using it
Note: by reading this notice you agree that all that is yours is mine, and all that is mine is mine also. ;-)
The license applies, wether you read it or not. The only difference is if you are aware that you are breaking it, or not.
Unless your use qualifies as fair use
(I know some jurisdictions have basic exceptions like "if you own software you can do what's needed to run it", but modifications?)
Not 100% related, but the copyright holder(s) are not clear. There is a list of authors so I'd bet they are the copyright holders. But given the fact their email addresses somewhat point to CMU, I wonder if CMU is behind...
However, the license specifically states that you cannot use it for sports. I wonder if they singed a high value exclusivity agreement with someone in that space, or if some such company funded the research originally...
"The non-exclusive commercial license cannot be used in the field of Sports. ("Sports" shall mean any and all athletic competition between individuals, groups of individuals or teams.)"