Paul,

I subscribe to GenealogyBank which has a newspaper database. I find "skedaddle" many times during the war starting in 1862, but never associated with 1st Manassas. After a quick search, I fail to find the expression "great skedaddle". You might have to check the several books on 1st Manassas/Bull Run in print and hope the author cites the source.

Best Regards,

Greg