Legal judgment prediction (LJP) is important for supporting judicial decision-making and improving judicial efficiency. Existing LLM-based approaches often rely on manually specified reasoning pipelines or external legal structures, while feedback-based methods typically provide generic signals of correctness or coherence rather than case-specific legal supervision. We propose IALR: Instance-Adaptive Legal Rubric Supervision for Legal Judgment Prediction. For each training instance, IALR contrasts model responses of varying quality and distills their legally consequential failures into a weighted Instance-Adaptive Legal Rubric. These rubrics convert judgment-relevant conditions into discriminative preference signals for Direct Preference Optimization, enabling the model to learn charge prediction without following a predefined reasoning paradigm. At inference time, IALR requires no additional evaluator or correction module. Experiments on four Chinese criminal charge-prediction benchmarks show that IALR consistently improves Qwen2.5-7B, yielding average absolute accuracy gains of 5.68% in-domain and 8.73% out-of-domain. These results demonstrate the effectiveness and cross-domain transferability of Instance-Adaptive Legal Rubric supervision. The code and data are available at https://github.com/Baii668/IALR.git.