Sanboxed happens in 2 ways. Google sandboxes some penalised site as a light penalty , you basically get put one side and rank far back for a while. In the sandbox you are under observation for any black hat techniques .
New websites also get sandboxed , because google assumes , you had a old website you have abandoned it so we dont know if we can trust you just yet.
Typically sandboxed sites wont appear on for queries , if you are new and sandboxed you can use google webmaster tools , and see when google starts processing your data and when you show up for a query .
If you have been penalised , stay clean , any further website penalties may cause a ban.