"According to the sandbox effect, links which may normally be weighted by Google's ranking algorithm, not least improving the position of a webpage in Google's index, may be subjected to filtering to prevent their having a full impact. Some observations have suggested that two important factors for causing this filter to come into play are the active age of a domain, and the competitiveness of the keywords used in links.
Active age of a domain should not be confused with the date of registration on a domain's WHOIS record, but instead refers to the time when Google first indexed pages on the domain. Keyword competitiveness refers to the search frequency of a word on Google search, with observation suggesting that the higher the search frequency of a word, the increasing likelihood that the sandbox filter effect will come into play."
In more simple terms, the penalty is if Google pins your page as any sort of spam, generally trying to manipulate Google's page ranking by creating lots of inbound links to a new web site from other web sites that you own...
You cant really control it, but to try and lessen the damage..
Actively gather content and good links, try to by old or expired domains, host on a well established host, increase traffic in other ways not related to google, Concentrate on less popular keywords... etc.
Google sandbox is nothing but an artificial delay technique that is used by the search engines to let the sites mature. It will delay the site ranking for 6 to 9 months unless you know how to get out of it.