Wis. Stat. § 907.01: Opinion testimony by lay witnesses.

If the witness is not testifying as an expert, the witness’s testimony in the form of opinions or inferences is limited to those opinions or inferences which are all of the following:

(1) Rationally based on the perception of the witness.

(2) Helpful to a clear understanding of the witness’s testimony or the determination of a fact in issue.

(3) Not based on scientific, technical, or other specialized knowledge within the scope of a witness under s. 907.02 (1).