[Handball / Penalty Kick] The ball strikes an arm raised to appeal for offside

Watch the movement of the Rennes defending player's arm. Whether that movement was natural or unnatural is the key to judging this handball offence. The footage shows that, as the cross from the free kick came in, the player raised an arm to appeal for offside. As the ball came close, the player tried to lower the outstretched arm, and the ball struck it. At the moment of contact, the arm was well away from the body, and the player had made their body unnaturally bigger. Taking all of this into account, the referee's decision to give a handball offence and award a penalty kick was reasonable and convincing, making this a good decision.