The reaction of stock prices of Italian football teams to the surprise factor in match outcomes

This paper examines how stock prices of Italian football clubs react to unexpected match outcomes, focusing on Juventus, Lazio, and Roma over the 2013–2014 to 2018–2019 football seasons. According to market efficiency theory, price adjustments should reflect only the “surprise” component of match results — that is, the deviation between the actual outcome and its ex-ante expectation. Using betting odds to proxy market expectations, we show that surprises exert a significant and immediate influence on stock prices, which is largely incorporated into opening prices on the first trading day after the match. By analysing both open and close prices, our findings indicate that some irregularities appear at market opening but tend to be corrected during the trading day, suggesting partial but not complete market efficiency. We also document asymmetric effects across clubs and explore whether rival-team results influence price adjustments. Overall, the results highlight the central role of expectation formation and surprise in shaping stock market reactions to sporting events.