This study examines how Form 144 filings, which are notices from company insiders planning to sell their shares, affect the stock market. We found that these filings lead to statistically significant changes in stock prices and the number of shares traded, especially for smaller companies. This suggests that the market may overreact to these filings. The research shows that the market's reaction can differ based on the size of the company and whether the information was already known or expected by investors. This work helps in understanding how insider trading can impact the fairness and efficiency of the market and suggests that it might be possible to produce portfolio returns by predicting these market changes. This study offers important insights for investors, regulators, and readers interested in the effectiveness of SEC filing requirements, and implements an approach to scraping for Form 144s.