Without being the admin? Probably not.
There's a few fundamental issues here.
Modern networks use switches, and switches only send data to the port where they're needed. If you specifically knew where to watch, and sneakily replaced a switch with a hub, and both you and the user torrenting were plugged in or you had the functionality for mirrored ports on the switch, you could. Otherwise, its not possible to monitor with another user is doing.
Not to mention that torrents use a range of ports, can be encrypted to obfuscate their nature....
If your actual issue is someone abusing the network for torrenting, and your network is slow due to that, talk to your network admin.
not to many people have hubs lying around... and people might notice the dramatic drop in speed ;) – Keltari – 2014-12-18T06:09:56.117
In which case, your suspect might be the person complaining ;p. I clean forgot hubs only came in basic, slow ethernet flavour – Journeyman Geek – 2014-12-18T06:11:32.143