Thanks both. It's an odd phrase, to me.

'Пехотный манипул попал в мешок'... I had thought it meant that they put Ratslayer into a sack after they had caught him. Is there something about this sentence that stops it from meaning that? Also, what case are 'манипул' and 'фланга'; they both look like genitive plural to me.

Thanks for the sack idea Medved, it sounds feasible; just a gap in the surrounding army, like a pocket, or something. Open at one end, until the enemy close it behind them. Putting 'by the way' in there would be a natural addition in this context.