According to Tom's old biography, at a young age he was exposed to a TV program in which a man brutally clubbed a baby seal, which inspired him to make such a game. Ironically, he disapproves of seal clubbing, and has said "Seal clubbing is wrong and anyone who participates in this activity (Canadians) should be shot."
The Club a Seal game led to some of the earliest hatemail in Newgrounds history. People called Tom Fulp a "SICK BASTARD," a "sad perverted sicko," and a "very sick young man." However, there were also a number of people who voiced their support. One player, a Newfoundland native, protested that clubbing seals was the most humane way to kill them, and mentioned how it was more humane than how cows were killed elsewhere.
The themes of violence and seals continued in Newgrounds culture long after Club A Seal was popular. Most notable is Clubby The Seal, a game that actual reverses the situation by allowing players to control a seal who skins humans. The game still seems to get quite a lot of viewers.