Hayden Greenbauer played safety. Looked comfortable, covered well, took on a couple of blockers and was in on at least one tackle.
Barnes looked pretty good. He has a really good frame (he's listed at 6-5, 215, but he looks a little thicker than that), and he should get a lot stronger. He plays with some power now, but he just looks like he could add a lot of size and strength if he moves into the weight room. In the "game" yesterday, he showed decent acceleration at the snap and got into the backfield a few times.
One other freshman to watch: before Wednesday's PonyFans LIVE show, Aldrick Robinson said he thinks freshman slot receiver Der'Rikk Thompson is faster than Robinson was as a freshman, and said Thompson will end up being faster before he graduates. Considering Robinson might be the fastest SMU player in 20 years (or is at least in the discussion, along with Brian Berry, Larry Wilson, Johnnie Freeman, Bryan McCann, etc.), that's saying a lot.
docabel is right about Randall Joyner: he flattened a couple of guys. One was the block on the receiver (Miller) who turned to chase Parks after his interception, and the other was on a tackle. Joyner can really hit.