Corrected entry: When Picard enters the bridge of the Scimitar, he hits a Reman with his Phaser rifle. The Reman drops and Picard sees that the rifle is broken from the impact. In "Insurrection" we saw Worf hit a metal probe with a similar rifle, and his rifle remained intact. Apparently weapons of the future are somewhat weaker then ours and while they can easily withstand the impact with a metal probe, the impact on a Reman skull is too much and it breaks.
Gary O'Reilly
12th Jun 2004
Correction: There are several possible explanations. Not all phaser rifles are the same, Worf may have had a stronger model (or even one customised for him to use as a mele weapon). The probe in Insurrection was most likely only covered with a very thin alloy and easily broken (they're not made for battle, merely to hover about). The Reman's skull may be incredibly thick, or maybe Picard's rifle was already damaged somewhat.
Gary O'Reilly