Upon his deathbed, Vsevolod the Big Nest bequeathed to him Pereslavl-Zalessky. In the conflict between his elder brothers Konstantin and Yuri, Yaroslav supported the latter. In 1215, he accepted the offer of the Novgorodians to become their prince but, desiring revenge for their former treachery, captured Torzhok and blocked its supplies of grain to Novgorod. Several months later, he was defeated by his father-in-law on the Lipitsa River and had to retreat to Pereslavl; a helmet that he lost during the battle would be retrieved by archaeologists in 1808.