Underdog of the Week is a Flash Portal award given to the submission with the highest difference between the Review score and the popular vote. Like the Review Crew Pick, this is an award which suggests a rather specialist/cult interest, leading to a smaller group of people giving the submission strong support. Again, like the RCP it is often won by a crew movie, where the crew has much more interest in it than the general voters of Newgrounds. It can only be won by a submission with over 30 reviews. This award has nothing to do with the Underdog List, which is a list of musicians on the Audio forums.
Good or Bad?
This award is often seen in a negative light by people who emphasise how it is won by people whose submissions are backed by their friends who give it high Reviews, but with a general score which is much lower. Others see it as a movie which appeals strongly to a certain niche of people and is good enough to get 30 people to bother to review it and give a high score, but one much higher than the general vote. These may not neccesarily be friends etc. but perhaps a category of people the movie was aiming for, such as fans of a subject.
Here is a discussion on the BBS by various people about Underdog, including considering its value.