Any object you hold which can cause death can be called a dangerous weapon. As chapter 939 section 22 states.
"Dangerous weapon" means any firearm, whether loaded or unloaded; any device designed as a weapon and capable of producing death or great bodily harm; any ligature or other instrumentality used on the throat, neck, nose, or mouth of another person to impede, partially or completely, breathing or circulation of blood; any electric weapon, as defined in s. 941.295(1c) (a); or any other device or instrumentality which, in the manner it is used or intended to be used, is calculated or likely to produce death or great bodily harm.
Skateboards can cause death or great bodily harm, especially when used on the head or neck area.
The defense did have a use of force expert who would have argued that use of the skateboard was assault, and would have clarified.
The expert, John Black, spent hours outlining the moments that led to Kyle Rittenhouse’s decisions to shoot Joseph Rosenbaum, Anthony Huber and Gaige Grosskreutz, offering a preview of the defense team’s strategy when Rittenhouse’s trial begins next month. Black testified that video shows Rosenbaum chasing Rittenhouse and reaching for the teenager’s gun, Huber attacking Rittenhouse with a skateboard and trying to wrestle away his gun, and Grosskreutz running at him with a pistol in his hand.
“A citizen in that position, given those indicators, would it be reasonable for them to believe they were about to be assaulted?” Black said. “I would argue yes.”
But his testimony was limited to content on time. so sadly we didn't get to see a professional discussion on the issue.
In trial, the defense attorney testified that skateboards could be used to behead people.
“Ladies and gentlemen, I would love to be able to hold up that skateboard in front of you as evidence today, because then you could see it,” Mr Richards told the jury. “You could see the weight and the heft of what a skateboard is, and what that skateboard would do if somebody takes it in their hand and swings down on somebody’s shoulder, head, and neck, trying to separate the head from the body.”
As Kraus replied in the prosecution rebuttal.
"Someone should tell all the parents and grandparents and Santa Claus giving skateboards this Christmas about how they're giving their children a deadly weapon. I guess they should get them an AR-15 instead."
Indicating that skateboards were children toys, not weapons.
It was as such left up to the jury, with no expert instructions and only prosecution and defense lawyer testimony, whether the skateboard was considered a deadly weapon.