Touchdown plays without WPA

[awgymer]

In the PBP data across all seasons there are over 400 good touchdown plays for which the WPA is <NA>. I have tried to find some common factor between them but there doesn't appear to be one. The home/away_wp_post are, logically, also <NA>. There are a further 500 + plays with <NA> WPA which are not TDs.

However, since TD plays are more likely to add significant WP I consider those to be the biggest concern, as it could conceivably skew any analysis.