Date: 201708
Local time of day: 0601-1200
Location: LAS.Airport, NV
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Ground LAS
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Communication Breakdown
Second reporter function: Pilot Flying; First Officer
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Flight Crew
When detected: Taxi
Result: General None Reported / Taken
Contributing factors: Airport; Human Factors; Procedure
Primary problem: Procedure

Narrative: It was the last leg.  We had an aircraft swap with preceding outbound aircraft at our gate; pushing late; so our arriving aircraft was holding out. When aircraft arrived at gate the entire Crew worked very well to turn the aircraft as close to on time as possible. We pushed four minutes late; not bad; all things considered. The taxi instructions were 'Spot 15 contact Ground Control'.  At Spot 15 we were told 'Give way to (other carrier) approaching from left and follow him via B; D to Runway 1R'. Neither of us could remember being told to hold short of Runway 26R. There were at least 20 aircraft ahead of us waiting for takeoff. Airport operations were landing and departing Runways 1L and 1R; and landing 26L.  99 percent of the arriving traffic was landing on 1L/1/R. In fact we only recalled one aircraft landing on Runway 26L and no one was departing to the west.  As we approached the taxiway intersection of Taxiways 'B' and 'D'; I heard Ground Control talking to a (other carrier) aircraft. The other carrier said that they required Runway 8L for departure.I can't remember the winds at the time; but I think there was a slight wind out of the east.  A few minutes later Ground Control informed him that Tower needed him airborne in two minutes; and that he should back-taxi down Runway 26R; (around all other aircraft on Taxiway 'B'); and plan to depart Runway 8L at A8. We had just made our turn to the south on Taxiway 'D' and I saw the (other carrier) aircraft back taxiing down Runway 26R and maneuvering to turn 180 degrees to depart to the east on Runway 8L. He was hurrying to make the two minute requirement that Ground Control had given him. (Other carrier) was told to contact Tower and I quickly realized that our nose of the aircraft was already over the hold short line for Runway 8L; but we were not across the runway. We were not on Tower frequency yet; so I asked the F/O to switch to Tower frequency to see if they had tried to call us even though we weren't quite to the switch over sign. I stopped the aircraft where we were and then Tower cleared (other carrier) to takeoff on Runway 8L; and the (other carrier) aircraft departed to the east. At no time were we instructed to hold short of Runway 8L by either Ground Control or Tower. However; Runway 8L had just become an active runway; at least from A8 intersection. The F/O and I monitored both frequencies of Ground and Tower to try and see if any other aircraft were being told to hold short of Runway 8L at Taxiway 'D'; but did not hear any. In a few minutes we were holding short of Runway 1R number one.  Tower cleared in 'Onto Hold'.  By the time we were turning into position for departure; tower cleared us for takeoff.  We departed to the north and the remainder of the flight was uneventful. Neither the F/O nor I think that we were ever instructed to hold short of Runway 8L; but the hurried departure of the (other carrier) aircraft on run Runway 8L was very confusing. We were not able to see where (other carrier) was until we made the turn onto Taxiway 'D'; and by then we were already past where I could see the hold short line. (Other carrier) was the only aircraft that we witnessed departing on Runway 8L in the 47 minutes that it took us to taxi out for departure. I think both Tower and Ground Control were rushing to get an 'Opposite Direction Departure' off in a very congested and time limited ATC environment and clarification on taxi instructions concerning our particular taxi clearance kinda became second to getting the (other carrier) airborne in the time limit. That's still no excuse for taxiing across a possible active runway without clearance.


Second narrative: [Report narrative contained no additional information.]


Synopsis: Flight Crew reported being uncertain of the taxi instructions from ground control; causing them to cross a hold short line of an active runway.