In Lent 1249 violence & looting of houses broke out, several people being killed and some students even went to Oxford to escape. This is one of the earliest recorded instances of the extreme form of Town-Gown rivalry.
Townsmen labelled students as "foreigners". Students grouped themselves as "Northerners" (England north of the River Trent), "Southerners", Welsh, Scots and so on.
North v. South battles were sometimes joined by townsmen, beggars and cut-throats, resulting in death and destruction. A series of such riots culminated in 1265/6 with the King dispatching justices to sort out the trouble. Local magistrates had hung some students and imprisoned or fined others.
As the University acquired privileges the rivalry tended to operate on two levels: the informal level plus a legal one. The town officials and the University spent a lot of time and money wrangling before Kings, Ministers and courts over rights and privileges. There was a respite on the legal side of about 80 years from around 1400.
Time and again the University would arrest someone who would then be released by a town official. The town kept trying to interfere in the University's operation of weights and measures checking on Stourbridge Fair. Mayors kept refusing to take the oath to uphold the University's privileges.
In the 1550s a joint "watch" of students and townsmen was set up, working in a rota, to keep order at the Fair. This worked for a while, so well that only the town watchmen were left on the streets and for sport the students started attacking the watchmen. It soon escalated. This lead to an order by the Senate that no scholar should be out of his college at night.
A third level of rivalry arose in the 1550s: Sir William Cecil, Chancellor of the University and Secretary of State versus the Duke of Norfolk and later Lord North, High Steward of the town.
In 1561 there was a new vogue: a football match between the townsmen of Chesterton and students was arranged. The referee was Thomas Parish, the head constable. On a signal the locals abandoned the game, got staves they'd hidden according to his instructions at the nearby St Giles church and beat up the students.
In 1783 it was reckoned that in the previous 14 years the Corporation had spent £480 on public services and 15 times that on litigation.
Things were relatively quiet for many years from around 1640 till an outbreak in 1827, with fireworks fired at police and University officials. Around this time there was an agricultural depression and student numbers had fallen, yet the population had increased. In 1825 the Vice-Chancellor promoted an Act for the Better Preservation of Peace and Good Order in the Universities of England, authorising him to appoint his own special constables for keeping the peace, prompted by the failure of the town's force. The University force lasted until 1856.
The Borough Police Force was created in 1836 and, being instantly recognisable in their uniforms and helmets, they became a favourite target for students.
There was serious undergraduate rioting in 1901 when the new underground toilets in the Market were opened and again in 1904 after the opening of the Downing Site labs by the King.
After years of peace, in 1944 at the by-now traditional 5th November student celebrations in the Market Square, British and US servicemen joined in and some damage to cars and windows was done. In 1954 things went further when some town yobbos set upon a student in spite of a massive police presence. A new townie sport of grad-bashing emerged: it applies to anyone looking like a student.