A breach of contract is a failure to do what the contract required.
Not every breach is the same
A minor failure that does not defeat the purpose of the agreement generally entitles the other side to compensation but not to walk away.
A material breach — one that defeats the point of the contract — may allow the other side to terminate and claim losses.
Which one it is decides everything about what can be done next, and it is frequently the whole of the dispute.
Cure periods
Many contracts require notice and a period to put it right before termination. Where one exists, terminating without following it can itself be the breach.
The commonest disputes in a service business
Scope. The customer expected something not in the agreement. This is why exclusions matter — see scope of work.
Payment. Work delivered and not paid for is a breach by the customer — see collections and, for property work, mechanic's lien.
Timing. Late completion, unless the contract made time critical and said so.
Changes. Work altered without a written variation, which is what change orders exist to prevent.
Force majeure
A clause excusing performance prevented by events outside either party's control. Whether a given event qualifies depends entirely on how the clause is drafted, and general wording is interpreted narrowly.
Cost increases and supply problems are usually not covered unless named.
What the injured party can recover
Generally the loss actually suffered, and there is usually a duty to mitigate rather than let it grow.
Legal costs are typically not recoverable unless the contract says so, which is why that clause matters on smaller amounts — recovering a modest debt can cost more than the debt.
Before acting
Terminating, withholding work, or refusing payment are all themselves potential breaches. Where the amount matters, this is a conversation with an attorney before acting rather than after.
Time limits
A claim has to be brought within a period set by law, which differs by state and by the kind of claim, and runs from a defined starting point rather than from when the problem was noticed.
Once it expires the claim is generally gone regardless of merit — the same unforgiving shape as lien deadlines.