"Against non-giant players and bots, the Sandman reduces move speed by 50% for short hits and 100% for moonshots (balls which travel for at least 1 second before hitting the victim).

Against giants, defined here as MiniBosses (true giants) and bots with a scale larger than 1.0 ("fake" giants), the Sandman behaves a bit differently. The amount of slowdown inflicted increases linearly with the ball's travel time, from 50% for short shots up to 75% for long shots. But right at the point of moonshots (1 second), the amount of slowdown jumps up from 75% to 100%.

Here's how slowdown is defined in this context: it's the percentage by which the player's movement speed is reduced, relative to the standard movement speed for that class in TF2. Most giants already have a 50% move speed penalty, so 50% slowdown doesn't actually affect them at all. (Slowdowns don't stack.) 75% slowdown effectively means that giants will move at half of their typical speed. And in all cases, 100% slowdown means that the player is unable to move at all.

(The degree of slowdown is separate from the matter of whether stun will prevent a player from using their weapons; true giants are able to use their weapons regardless of whether they are stunned. Also note that bots are able to jump even when stunned, if they think they are "stuck" because they haven't moved recently.)"