Cross-cutting commenting on social media is often imagined as a path to deliberation, yet exposure to opposing views frequently fuels hostility. To explain this dynamic, we introduce the concept of partisan warriors--commenters who cross ideological lines primarily to launch uncivil attacks against out-partisans. We analyze a large corpus of YouTube comments (N= 1,854,320) surrounding the 2024 U.S. second presidential debate. After filtering for toxicity and active participation, we use large language models to identify attack targets and operationalize partisan warrior behavior. Our analysis highlights four dynamics. First, cross-cutting commenters do not exhibit greater civility than those who remain within their ideological camps (RQ1). Second, audience reactions diverge by ideology: conservative audiences tended to reward hostile attacks on out-group leaders, whereas liberal audiences offered no comparable incentives and at times penalized such attacks (RQ2). Third, partisan warriors are notably more prevalent in conservative-leaning channels than in liberal ones; commenters restricted to conservative spaces were substantially more likely to engage in partisan warrior behavior compared to their liberal-only counterparts (RQ3). Finally, regarding environmental triggers, robustness checks suggest that this participation is an ecological phenomenon driven largely by channel-level heterogeneity rather than transient responses to individual video titles (RQ4). By shifting attention from the prevalence of incivility to its targets, rewards, and structural drivers, this study advances understanding of how partisan hostility is enacted and sustained in online spaces.

翻译：社交媒体上的跨阵营评论常被设想为通往理性对话的路径，然而接触对立观点往往助长敌对情绪。为解释这一动态，我们引入"党派战士"概念——指主要出于对异见者发起不文明攻击而跨越意识形态界限的评论者。我们分析了围绕2024年美国第二次总统辩论的大量YouTube评论语料库（N=1,854,320）。在筛选毒性言论与活跃参与者后，采用大语言模型识别攻击目标并操作化定义党派战士行为。我们的分析揭示了四种动态：第一，跨阵营评论者并未展现出比固守本阵营者更高程度的文明性（研究问题1）。第二，受众反应呈现意识形态分化：保守派受众倾向于奖励针对外群体领袖的敌意攻击，而自由派受众既未提供类似激励，有时甚至对此类攻击施加惩罚（研究问题2）。第三，党派战士在保守倾向频道中的出现频率显著高于自由派频道；相较于仅活跃于自由派空间的评论者，仅活跃于保守派空间的评论者参与党派战士行为的可能性显著更高（研究问题3）。第四，关于环境触发因素，稳健性检验表明这种参与主要由频道层面的异质性驱动，而非对个别视频标题的瞬时反应，呈现生态性现象特征（研究问题4）。通过将研究重心从失范行为的普遍性转向其攻击对象、激励方式与结构性驱动因素，本研究推进了对党派敌意在网络空间中如何被实施与维持的理解。