A driver of a U-Haul truck carrying beer kegs through a tailgating area before the Yale-Harvard game Saturday suddenly accelerated, fatally striking a 30-year-old Massachusetts woman and injuring two other women, police said. It’s not clear why the driver sped up, New Haven Police spokesman David Hartman said. The truck then crashed into other U-Haul vans in the lot, an open playing field used for pre-game tailgating parties before Yale home games in New Haven.