Mr. Strong (D) was a member of the Brotherhood of Maintenance of Way Employees. A 1973 Agreement provided that the Supplemental Sickness Benefits (SSB) received by employees would not duplicate recovery of lost wages from a disability case. D was injured in two separate accidents on September 12, 1983, and March 5, 1985, during his employment with P. He brought suit against P to recover for these injuries under the Federal Employers Liability Act (FELA), 45 U.S.C. §§ 51-60. Following a jury trial, D was awarded $73,000 in compensation for the 1983 injury; P was found not liable for the 1985 injury. After the trial, P moved for a determination that the amount of the judgment ought to be reduced by $11,678.21, the amount paid to D in SSB benefits. The district court held that 'in the absence of a lien or judgment in its favor, [Burlington] is not entitled to withhold the sum of $11,678.21 for any Supplemental Sickness Benefit paid to [Mr. Strong].' The district court suggested that D could not succeed in keeping the money if P sued on the contract. P sued on the contract to recover the SSB payments. D argued that the railroad's suit was barred by res judicata because such a claim should have been brought as a compulsory counterclaim to the previous FELA suit. However, the court decided that the railroad's claim was a permissive, not compulsory, counterclaim: 'Burlington Northern's right to recoup the disability benefits does not arise out of the same occurrence (the accidents) that gave rise to Strong's lawsuit; it derives from the provisions of the Supplemental Sickness Benefit Agreement of May 12, 1973.' The court further decided that, even if the claim could be said to be related to the same occurrence, an exception for claims that had not matured at the time of filing the answer would apply. P's motion for summary judgment was granted. D appealed.