After being placed on probation (called "community supervision" in statutes), the prosecuting attorney may file a "motion to revoke" probation, alleging that the probationer violated the conditions of probation.
Probationers often wrongly assume that a probation officer can "revoke" them. Revocation can occur only after a motion has been filed, served on the probationer, and after the probationer has had an opportunity to defend himself against the allegations in the motion.
The government is then required to prove the probationer violated the conditions of his probation. No jury trial will occur; this hearing is before the sentencing judge. The proof requirement is a "preponderance", meaning it is more likely than not that the violation happened.
For example, a probationer who was required not to commit any crimes gets arrested for possession of marijuana. The government can win only if it can prove that it is more likely than not that the probationer intended or knew he was in possession of a substance he knew to be marijuana. The burden is the same as a regular lawsuit, like an automobile accident damages case.
The probationer also has many rights at a revocation hearing. For example, probationers can subpoena witnesses and evidence, as well as cross-examine witnesses against him.
If the government proves the probationer violated probation conditions, the case is not necessarily finished; violation of probation does not automatically equal prison or jail. The judge has many options, including extending the length of probation, imposing an additional fine, requiring counseling, boot camp, and requiring the probationer to submit to drug or alcohol treatment programs.
At its most basic level, most probations are somewhat like contracts between the judge and the probationer. The judge agrees not to imprison the probationer for as long as he could, and the probationer agrees to abide by rules the judge sets. Conditions of probation vary greatly and can even include significant jail time.
Certain technical defenses exist that could prevent revocation, even when violations have occurred.
This description is not meant to make probationers comfortable when a motion to revoke is filed against them, but it is important that the probationer not lose hope. A qualified attorney may very well be able to provide valuable assistance.