The early medieval period is a long time which sees the rise and fall of many different English polities, so for the sake of convenience, let's say that you're a ceorl or (slightly anachronistically) a villein in 9th or 10th Century Wessex, and subject to the laws of Alfred the Great. These are presented in full in both English and Old English in Attenborough's The Laws of the Earliest English Kings.

Let us also assume that you have, in fact, assaulted your neighbour, and are not the victim of a bizarre legal hoax. It wouldn't be in anybody's interest to falsely accuse you; if you were unfairly detained, you would be liable to 10 shillings compensation, a considerable sum. If during your arrest, your hair or beard had been cut, you'd receive a further 10 and 20 shillings respectively. Beards are serious business.

Assuming you weren't apprehended at the scene, the plaintiff would bring their case before the reeve, at one of the regular hundred-level meetings which they were legally required to hold in order to dispense justice. There, he might be expected to provide evidence of the assault and swear on oath that you were the attacker. Of course, if you had been apprehended at the scene, or arrested after by the reeve's men - or perhaps the local fyrd - you would be detained either by members of your community or at a royal manor. You could effectively be placed under house arrest for up to a month awaiting trial, but if your plaintiff and his family, or the wider community, didn't have the ability to enforce this then they could ask the local ealdorman or reeve to provide assistance, as was part of his responsibilities.

If you assaulted and injured somebody, you would be liable to pay them a weregild as well as a fine to the authorities, although the weregild would not be as substantial as if you had killed somebody. Weregild (literally 'person money') is essentially a statutory compensation applicable at every level of society designed to prevent feud by providing recompense for a victim of crime or their family. This developed into a sophisticated system for a variety of infractions, and was often accompanied by a series of additional fines. If you fought in somebody else's house, for example - perhaps a fellow villager selling ale - then you'd also be liable to pay them 6 shillings compensation as well. You'd better hope you didn't start a fight in front of one of the ealdorman's lieutenants - in which case you'd be liable for a further fine of some 30 shillings - or the ealdorman himself, which would land you a fine of 100 shillings. If you fought at a royal manor, you might even be put to death.

Alfred's laws have a fairly sophisticated system of weregilds and fines, covering everything from murder and assault, to rape, various degrees of sexual assault and harassment, breaking and entering, and even aiding and abetting. In particular, there is a fairly extensive list of various injuries you may have inflicted and the weregild for each one:

A head laceration would invoke a shilling compensation; a facial wound, 2 shillings. If you fracture the skull or jaw, you'd be liable for 15 shillings, or 30 if you fractured both. A broken rib would cost you 10 shillings, a broken arm 15 shillings per bone. If you managed to deafen somebody, you'd be liable for 60 shillings, and 44 shillings and 4d if you blinded them in one eye. Each front tooth would cost you 8 shillings, an incisor 15, and a molar 4. Once weapon injuries get involved, things get expensive. You'd be liable for 30 shillings per stab would, for example. Paralysing somebody would cost you at minimum 100 shillings, although it's suggested that the court could fine you much more if they felt it was appropriate. In a way, these fines are here to protect you; if you could not pay, then your family would be liable. If they couldn't pay either, then you might be liable to penal slavery, or, more commonly be liable to feud.