As network television’s top scripted series, CBS’ “The Big Bang Theory” rarely commands negative attention in its ratings reports.

And, from a big picture perspective, it should not do so this week. It was Thursday’s top-rated show by a significant margin.

It did, however, reveal vulnerability to the ratings downfall that has been powerfully affecting virtually every show on television this spring.

Save for a notable adjustment in the finals, Thursday’s adults 18-49 rating will rank as the show’s weakest since 2011.

Facing competition from the NFL Draft and the spring ratings bug, the season’s penultimate “Big Bang Theory” episode slipped to a 3.7 adults 18-49 rating with 14.17 million viewers. The performance was down significantly from that of last week’s telecast, which drew a 4.4 with 15.68 million viewers in the comparable fast nationals.

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