Is it legal for a team to make a mechanism that is solely built to purposefully grasp, grapple, or entangle their teammate robot? If this mechanism, as a second hand as a backup strategy, gets used to purposefully grasp, grapple, or entangle opponents robots while center parked, would this also be a legal strategy?
Official Q&A: VRC 2018-2019: Turning Point
150: Clarification on damage and entanglement
As always, it is impossible to issue a blanket ruling on a hypothetical design. In addition to the first line of G12, the other main rule to consider would be R3, quoted here for reference:
<R3> The following types of mechanisms and components are NOT allowed:
a. Those that could potentially damage playing field components.
b. Those that could potentially damage other competing robots.
c. Those that pose an unnecessary risk of entanglement.
Any mechanism which is designed primarily to Entangle partner Robots, and secondarily to Entangle opponent Robots, could be at risk of violating R3b and/or R3c, depending on the specific nature of the mechanism.
As mentioned in this Q&A post, there are no rules against Entanglement between Robots on the same Alliance. If attempting such a strategy, the best way for Teams to avoid potential issues with R3 and/or G12 would be to protect these hypothetical mechanisms from opponent interaction, or otherwise proactively ensure that they are primarily used for offense, not defense.